display.texi

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990-1995, 1998-2015 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Display
@chapter Emacsの画面表示

本章では、Emacsがユーザーに提示する画面表示に関連する
さまざまな機能について述べます。

@menu
* Refresh Screen::      Clearing the screen and redrawing everything on it.
* Forcing Redisplay::   Forcing redisplay.
* Truncation::          Folding or wrapping long text lines.
* The Echo Area::       Displaying messages at the bottom of the screen.
* Warnings::            Displaying warning messages for the user.
* Invisible Text::      Hiding part of the buffer text.
* Selective Display::   Hiding part of the buffer text (the old way).
* Temporary Displays::  Displays that go away automatically.
* Overlays::            Use overlays to highlight parts of the buffer.
* Size of Displayed Text::  How large displayed text is.
* Line Height::         Controlling the height of lines.
* Faces::               A face defines a graphics style for text characters:
                          font, colors, etc.
* Fringes::             Controlling window fringes.
* Scroll Bars::         Controlling scroll bars.
* Window Dividers::     Separating windows visually.
* Display Property::    Enabling special display features.
* Images::              Displaying images in Emacs buffers.
* Buttons::             Adding clickable buttons to Emacs buffers.
* Abstract Display::    Emacs's Widget for Object Collections.
* Blinking::            How Emacs shows the matching open parenthesis.
* Character Display::   How Emacs displays individual characters.
* Beeping::             Audible signal to the user.
* Window Systems::      Which window system is being used.
* Bidirectional Display:: Display of bidirectional scripts, such as
                             Arabic and Farsi.
@end menu

@node Refresh Screen
@section スクリーン全体の再表示
@cindex リフレッシュスクリーン
@cindex スクリーンのリフレッシュ

関数@code{redraw-frame}は、指定したフレーム（@pxref{Frames}）の
内容全体をクリアし再表示します。この関数は画面が破壊された時に便利です。

@defun redraw-frame frame
この関数は、フレーム@var{frame}をクリアしてから再表示する。
@end defun

より強力なのは@code{redraw-display}です。

@deffn Command redraw-display
この関数は、すべての可視フレームをクリアしてから再表示する。
@end deffn

ユーザー入力の処理のほうが再表示より絶対的に優先します。
入力があるときにこれらの関数を呼び出してもただちにはなにもしませんが、
入力をすべて処理し終えてから再表示します。

通常、Emacsを停止したり再開しても
スクリーン全体を再表示します。
Emacsのようなディスプレイ向けプログラムと通常の逐次表示向けに、
表示内容を個別に記録できる端末エミュレータもあります。
そのような端末を使っているときには、
再開時の再表示を禁止した場合もあります。

@defopt no-redraw-on-reenter
@cindex 停止（@code{no-redraw-on-reenter}を参照 ）
@cindex 再開（@code{no-redraw-on-reenter}を参照 ）
この変数は、停止後に再開したあとで、
スクリーン全体を再表示するかどうかを制御する。
@code{nil}以外であると再描画の必要はないことを意味し、
@code{nil}であると再描画が必要であることを意味する。
デフォルトは@code{nil}である。
@end defopt

@node Forcing Redisplay
@section Forcing Redisplay
@cindex forcing redisplay

  Emacs normally tries to redisplay the screen whenever it waits for
input.  With the following function, you can request an immediate
attempt to redisplay, in the middle of Lisp code, without actually
waiting for input.

@defun redisplay &optional force
This function tries immediately to redisplay.  The optional argument
@var{force}, if non-@code{nil}, forces the redisplay to be performed,
instead of being preempted if input is pending.

The function returns @code{t} if it actually tried to redisplay, and
@code{nil} otherwise.  A value of @code{t} does not mean that
redisplay proceeded to completion; it could have been preempted by
newly arriving input.
@end defun

@defvar pre-redisplay-function
A function run just before redisplay.  It is called with one argument,
the set of windows to redisplay.
@end defvar

  Although @code{redisplay} tries immediately to redisplay, it does
not change how Emacs decides which parts of its frame(s) to redisplay.
By contrast, the following function adds certain windows to the
pending redisplay work (as if their contents had completely changed),
but does not immediately try to perform redisplay.

@defun force-window-update &optional object
This function forces some or all windows to be updated the next time
Emacs does a redisplay.  If @var{object} is a window, that window is
to be updated.  If @var{object} is a buffer or buffer name, all
windows displaying that buffer are to be updated.  If @var{object} is
@code{nil} (or omitted), all windows are to be updated.

This function does not do a redisplay immediately; Emacs does that as
it waits for input, or when the function @code{redisplay} is called.
@end defun

@node Truncation
@section 表示の切り詰め
@cindex 行の折り返し
@cindex 行の切り詰め
@cindex 継続行
@cindex @samp{$}、画面表示
@cindex @samp{\}、画面表示

テキスト行がウィンドウの右端を越えていると、
Emacsはその行を次のスクリーン行へ@dfn{継続する}
（次の行に『折り返し』する）か、スクリーン行1行に@dfn{切り詰め}
（一行以内に収め）ます。
長いテキスト行を表示するために使われる追加のスクリーン行を
@dfn{継続}行と呼びます。
継続することと詰め込みは別のことです。
継続はスクリーン上だけのことであり、バッファ内容は変わりません。
また、継続では単語の境界ではなく、正確にスクリーンの右端で
行を分けます。
@xref{Filling}。

グラフィック表示では、ウィドウの端に、小さな矢印の画像が表示され、継続または
切り詰めを示します（@pxref{Fringes}）。
テキスト端末では、ウィンドウの最右端のコラムに現れる@samp{$}で切り詰めたことを示し、
@samp{\}でつぎの行に『折り返した』ことを示します。
（表示テーブルで別の文字を指定できる。
@pxref{Display Tables}。）

@defopt truncate-lines
このバッファローカルな変数が@code{nil}でなければ、
ウィンドウの右端を越える行は切り詰められる。
それ以外なら、行は継続される。
特別な例外として、
@dfn{部分幅ウィンドウ}の（フレーム全体の幅を専有しないウィンドウ）では、
変数@code{truncate-partial-width-windows}が優先される。
@end defopt

@defopt truncate-partial-width-windows
@cindex partial-width windows
この変数は、@dfn{部分幅ウィンドウ}の行の切り詰めを制御する。
部分幅ウィンドウは、フレーム全体の幅を専有しないウィンドウである（@pxref{Splitting Windows}）。
値が@code{nil}ならば、行の切り詰めは@code{truncate-lines}（上記参照）で決まる。
値が整数@var{n}ならば、@code{truncate-lines}の値に関係なく、
部分幅ウィンドウが @var{n}以下の場合に行を切り詰める。
部分幅ウィンドウが@var{n}以上のカラムを持つ場合、行の切り詰めは
@code{truncate-lines}によって決定される。
それ以外の@code{nil}でない値では、
@code{truncate-lines}に関係なく全ての部分幅ウィンドウで行が切り詰められる。
@end defopt

ウィンドウが水平方向スクロール（@pxref{Horizontal Scrolling}）する場合は、
強制的に切り詰められる。

@defvar wrap-prefix
If this buffer-local variable is non-@code{nil}, it defines a
@dfn{wrap prefix} which Emacs displays at the start of every
continuation line.  (If lines are truncated, @code{wrap-prefix} is
never used.)  Its value may be a string or an image (@pxref{Other
Display Specs}), or a stretch of whitespace such as specified by the
@code{:width} or @code{:align-to} display properties (@pxref{Specified
Space}).  The value is interpreted in the same way as a @code{display}
text property.  @xref{Display Property}.

A wrap prefix may also be specified for regions of text, using the
@code{wrap-prefix} text or overlay property.  This takes precedence
over the @code{wrap-prefix} variable.  @xref{Special Properties}.
@end defvar

@defvar line-prefix
If this buffer-local variable is non-@code{nil}, it defines a
@dfn{line prefix} which Emacs displays at the start of every
non-continuation line.  Its value may be a string or an image
(@pxref{Other Display Specs}), or a stretch of whitespace such as
specified by the @code{:width} or @code{:align-to} display properties
(@pxref{Specified Space}).  The value is interpreted in the same way
as a @code{display} text property.  @xref{Display Property}.

A line prefix may also be specified for regions of text using the
@code{line-prefix} text or overlay property.  This takes precedence
over the @code{line-prefix} variable.  @xref{Special Properties}.
@end defvar

@ignore
バッファが非常に短い行しかない場合は、
@code{cache-long-scans}を@code{nil}に設定するのがよいです。

@defvar cache-long-scans
この変数が@code{nil}以外（デフォルト）であると、
字下げ／移動関数とEmacsの再表示において、
バッファを走査した結果をキャッシュし、
バッファが変更されていないときには
キャッシュを調べてバッファの対象領域の再走査を回避する。

キャッシュするようにすると、短い行の処理が多少遅くなる。

この変数は、すべてのバッファで自動的にバッファローカルである。
@end defvar
@end ignore

@node The Echo Area
@section エコー領域
@cindex エコー表示
@cindex エコー領域

@c FIXME: Why not use @xref{Minibuffers} directly?  --xfq
@dfn{エコー領域}（echo area）は、
（@pxref{Errors}）エラーを表示したり
基本関数@code{message}でメッセージを表示したり、
打鍵を表示するために使われます。
（活性な）ミニバッファはエコー領域と
同じスクリーン上の位置に現れますが、
エコー領域とミニバッファは同じものではありません。
@xref{Minibuffer,, The
Minibuffer, emacs, The GNU Emacs Manual}。

本節で解説されている関数以外でも、ストリームとして
@code{t}を指定することで、Lispオブジェクトをエコー領域に
表示できます。@xref{Output Streams}。

@menu
* Displaying Messages:: Explicitly displaying text in the echo area.
* Progress::            Informing user about progress of a long operation.
* Logging Messages::    Echo area messages are logged for the user.
* Echo Area Customization:: Controlling the echo area.
@end menu

@node Displaying Messages
@subsection Displaying Messages in the Echo Area
@cindex display message in echo area

  This section describes the standard functions for displaying
messages in the echo area.

@defun message format-string &rest arguments
この関数は、エコー領域に1行のメッセージを表示する。
引数@var{format-string}は、@code{format}と同様の書式文字列
（@pxref{Formatting Strings}）であり、
@var{arguments}は書式指定で表示されるオブジェクトである。
結果としての整形された文字列はエコー領域に表示される。
@code{face}テキスト属性を持つ場合、
指定されたフェイスで表示される（@pxref{Faces}）。
文字列はまた@file{*Messages*}バッファにも追加されるが、
テキストプロパティは除去される（@pxref{Logging Messages}）。

バッチモードでは、メッセージは改行と共に
標準エラーストリームへ出力される。

When @code{inhibit-message} is non-@code{nil}, no message will be displayed
in the echo area, it will only be logged to @samp{*Messages*}.

@var{format-string}が@code{nil}または空文字列ならば、
@code{message}はエコー領域をクリアする。
エコー領域が自動的に拡張されている場合は、通常サイズに戻される。
ミニバッファが活性であると、
これによりミニバッファの内容がスクリーンにただちに表示し直される。

@example
@group
(message "Minibuffer depth is %d."
         (minibuffer-depth))
 @print{} Minibuffer depth is 0.
@result{} "Minibuffer depth is 0."
@end group

@group
---------- Echo Area ----------
Minibuffer depth is 0.
---------- Echo Area ----------
@end group
@end example

To automatically display a message in the echo area or in a pop-buffer,
depending on its size, use @code{display-message-or-buffer} (see below).
@end defun

@defvar inhibit-message
When this variable is non-@code{nil}, @code{message} and related functions
will not use the Echo Area to display messages.
@end defvar

@defmac with-temp-message message &rest body
This construct displays a message in the echo area temporarily, during
the execution of @var{body}.  It displays @var{message}, executes
@var{body}, then returns the value of the last body form while restoring
the previous echo area contents.
@end defmac

@defun message-or-box format-string &rest arguments
この関数は@code{message}と同様にメッセージを表示するが、
エコー領域のかわりに対話ボックスを使うこともある。
この関数がマウスを用いて起動されたコマンドから呼ばれたとき、
より正確には、@code{last-nonmenu-event}（@pxref{Command Loop Info}）が
@code{nil}かリストのいずれかであると、
メッセージを表示するために対話ボックスかポップアップメニューを用いる。
さもなければエコー領域を用いる。
（これは、同様な決定をくだす@code{y-or-n-p}の判定条件と同じである。
@ref{Yes-or-No Queries}参照。）

呼び出しの周りで@code{last-nonmenu-event}に適切な値を束縛することで、
マウスを使うかエコー領域を使うか強制できる。
@end defun

@defun message-box format-string &rest arguments
@anchor{message-box}
この関数は@code{message}と同様にメッセージを表示するが、
可能な限り対話ボックス（やポップアップメニュー）を使う。
対話ボックスやポップアップメニューを扱えない端末などで
これらを使用できない場合には、
@code{message-box}は@code{message}と同様にエコー領域を使う。
@end defun

@defun display-message-or-buffer message &optional buffer-name not-this-window frame
This function displays the message @var{message}, which may be either a
string or a buffer.  If it is shorter than the maximum height of the
echo area, as defined by @code{max-mini-window-height}, it is displayed
in the echo area, using @code{message}.  Otherwise,
@code{display-buffer} is used to show it in a pop-up buffer.

Returns either the string shown in the echo area, or when a pop-up
buffer is used, the window used to display it.

If @var{message} is a string, then the optional argument
@var{buffer-name} is the name of the buffer used to display it when a
pop-up buffer is used, defaulting to @file{*Message*}.  In the case
where @var{message} is a string and displayed in the echo area, it is
not specified whether the contents are inserted into the buffer anyway.

The optional arguments @var{not-this-window} and @var{frame} are as for
@code{display-buffer}, and only used if a buffer is displayed.
@end defun

@defun current-message
この関数は、エコー領域に現在表示されているメッセージを返す。
なければ@code{nil}を返す。
@end defun

@node Progress
@subsection Reporting Operation Progress
@cindex progress reporting

  When an operation can take a while to finish, you should inform the
user about the progress it makes.  This way the user can estimate
remaining time and clearly see that Emacs is busy working, not hung.
A convenient way to do this is to use a @dfn{progress reporter}.

  Here is a working example that does nothing useful:

@smallexample
(let ((progress-reporter
       (make-progress-reporter "Collecting mana for Emacs..."
                               0  500)))
  (dotimes (k 500)
    (sit-for 0.01)
    (progress-reporter-update progress-reporter k))
  (progress-reporter-done progress-reporter))
@end smallexample

@defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
This function creates and returns a progress reporter object, which
you will use as an argument for the other functions listed below.  The
idea is to precompute as much data as possible to make progress
reporting very fast.

When this progress reporter is subsequently used, it will display
@var{message} in the echo area, followed by progress percentage.
@var{message} is treated as a simple string.  If you need it to depend
on a filename, for instance, use @code{format} before calling this
function.

The arguments @var{min-value} and @var{max-value} should be numbers
standing for the starting and final states of the operation.  For
instance, an operation that ``scans'' a buffer should set these to the
results of @code{point-min} and @code{point-max} correspondingly.
@var{max-value} should be greater than @var{min-value}.

Alternatively, you can set @var{min-value} and @var{max-value} to
@code{nil}.  In that case, the progress reporter does not report
process percentages; it instead displays a ``spinner'' that rotates a
notch each time you update the progress reporter.

If @var{min-value} and @var{max-value} are numbers, you can give the
argument @var{current-value} a numerical value specifying the initial
progress; if omitted, this defaults to @var{min-value}.

The remaining arguments control the rate of echo area updates.  The
progress reporter will wait for at least @var{min-change} more
percents of the operation to be completed before printing next
message; the default is one percent.  @var{min-time} specifies the
minimum time in seconds to pass between successive prints; the default
is 0.2 seconds.  (On some operating systems, the progress reporter may
handle fractions of seconds with varying precision).

This function calls @code{progress-reporter-update}, so the first
message is printed immediately.
@end defun

@defun progress-reporter-update reporter &optional value
This function does the main work of reporting progress of your
operation.  It displays the message of @var{reporter}, followed by
progress percentage determined by @var{value}.  If percentage is zero,
or close enough according to the @var{min-change} and @var{min-time}
arguments, then it is omitted from the output.

@var{reporter} must be the result of a call to
@code{make-progress-reporter}.  @var{value} specifies the current
state of your operation and must be between @var{min-value} and
@var{max-value} (inclusive) as passed to
@code{make-progress-reporter}.  For instance, if you scan a buffer,
then @var{value} should be the result of a call to @code{point}.

This function respects @var{min-change} and @var{min-time} as passed
to @code{make-progress-reporter} and so does not output new messages
on every invocation.  It is thus very fast and normally you should not
try to reduce the number of calls to it: resulting overhead will most
likely negate your effort.
@end defun

@defun progress-reporter-force-update reporter &optional value new-message
This function is similar to @code{progress-reporter-update} except
that it prints a message in the echo area unconditionally.

The first two arguments have the same meaning as for
@code{progress-reporter-update}.  Optional @var{new-message} allows
you to change the message of the @var{reporter}.  Since this function
always updates the echo area, such a change will be immediately
presented to the user.
@end defun

@defun progress-reporter-done reporter
This function should be called when the operation is finished.  It
prints the message of @var{reporter} followed by word ``done'' in the
echo area.

You should always call this function and not hope for
@code{progress-reporter-update} to print ``100%''.  Firstly, it may
never print it, there are many good reasons for this not to happen.
Secondly, ``done'' is more explicit.
@end defun

@defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
This is a convenience macro that works the same way as @code{dotimes}
does, but also reports loop progress using the functions described
above.  It allows you to save some typing.

You can rewrite the example in the beginning of this node using
this macro this way:

@example
(dotimes-with-progress-reporter
    (k 500)
    "Collecting some mana for Emacs..."
  (sit-for 0.01))
@end example
@end defmac

@node Logging Messages
@subsection Logging Messages in @file{*Messages*}
@cindex logging echo-area messages

  Almost all the messages displayed in the echo area are also recorded
in the @file{*Messages*} buffer so that the user can refer back to
them.  This includes all the messages that are output with
@code{message}.  By default, this buffer is read-only and uses the major
mode @code{messages-buffer-mode}.  Nothing prevents the user from
killing the @file{*Messages*} buffer, but the next display of a message
recreates it.  Any Lisp code that needs to access the
@file{*Messages*} buffer directly and wants to ensure that it exists
should use the function @code{messages-buffer}.

@defun messages-buffer
This function returns the @file{*Messages*} buffer.  If it does not
exist, it creates it, and switches it to @code{messages-buffer-mode}.
@end defun

@defopt message-log-max
この変数は、バッファ@file{*Messages*}に保持する行数を指定する。
値@code{t}は、保持する行数を制限しないことを意味する。
値@code{nil}は、メッセージをまったく記録しないことを意味する。
メッセージを表示しつつそれを記録しないようにするには
つぎのようにする。

@example
(let (message-log-max)
  (message @dots{}))
@end example
@end defopt

  To make @file{*Messages*} more convenient for the user, the logging
facility combines successive identical messages.  It also combines
successive related messages for the sake of two cases: question
followed by answer, and a series of progress messages.

  A ``question followed by an answer'' means two messages like the
ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
and the second is @samp{@var{question}...@var{answer}}.  The first
message conveys no additional information beyond what's in the second,
so logging the second message discards the first from the log.

  A ``series of progress messages'' means successive messages like
those produced by @code{make-progress-reporter}.  They have the form
@samp{@var{base}...@var{how-far}}, where @var{base} is the same each
time, while @var{how-far} varies.  Logging each message in the series
discards the previous one, provided they are consecutive.

  The functions @code{make-progress-reporter} and @code{y-or-n-p}
don't have to do anything special to activate the message log
combination feature.  It operates whenever two consecutive messages
are logged that share a common prefix ending in @samp{...}.

@node Echo Area Customization
@subsection Echo Area Customization
@cindex echo area customization

  These variables control details of how the echo area works.

@defvar cursor-in-echo-area
この変数は、エコー領域にメッセージを表示しているときに
カーソルをどこに表示するかを制御する。
@code{nil}以外であると、メッセージの末尾にカーソルを表示する。
さもなければ、エコー領域にではなく、ポイント位置にカーソルを表示する。

この値は普通は@code{nil}である。
Lispプログラムはこれに@code{t}を短い期間だけ束縛する。
@end defvar

@defvar echo-area-clear-hook
このノーマルフックは、@code{(message nil)}や他の理由で
エコー領域をクリアするたびに実行される。
@end defvar

@defopt echo-keystrokes
この変数は、コマンド文字を表示するまでの経過時間を決定する。
この値は整数であり、表示し始めるまでに待つ秒数を指定する。
ユーザーが（@kbd{C-x}などの）プレフィックスキーを打ってから
つぎを打つまでにこの秒数だけ遅れがあると、
プレフィックスキーをエコー領域に表示する。
（いったんキー列の表示を始めると、
同じキー列の以降の文字すべてを表示する。）

値がゼロであると、コマンド入力を表示しない。
@end defopt

@defvar message-truncate-lines
Normally, displaying a long message resizes the echo area to display
the entire message.  But if the variable @code{message-truncate-lines}
is non-@code{nil}, the echo area does not resize, and the message is
truncated to fit it.
@end defvar

  The variable @code{max-mini-window-height}, which specifies the
maximum height for resizing minibuffer windows, also applies to the
echo area (which is really a special use of the minibuffer window;
@pxref{Minibuffer Misc}).

@node Warnings
@section Reporting Warnings
@cindex warnings

  @dfn{Warnings} are a facility for a program to inform the user of a
possible problem, but continue running.

@menu
* Warning Basics::      Warnings concepts and functions to report them.
* Warning Variables::   Variables programs bind to customize their warnings.
* Warning Options::     Variables users set to control display of warnings.
* Delayed Warnings::    Deferring a warning until the end of a command.
@end menu

@node Warning Basics
@subsection Warning Basics
@cindex severity level

  Every warning has a textual message, which explains the problem for
the user, and a @dfn{severity level} which is a symbol.  Here are the
possible severity levels, in order of decreasing severity, and their
meanings:

@table @code
@item :emergency
A problem that will seriously impair Emacs operation soon
if you do not attend to it promptly.
@item :error
A report of data or circumstances that are inherently wrong.
@item :warning
A report of data or circumstances that are not inherently wrong, but
raise suspicion of a possible problem.
@item :debug
A report of information that may be useful if you are debugging.
@end table

  When your program encounters invalid input data, it can either
signal a Lisp error by calling @code{error} or @code{signal} or report
a warning with severity @code{:error}.  Signaling a Lisp error is the
easiest thing to do, but it means the program cannot continue
processing.  If you want to take the trouble to implement a way to
continue processing despite the bad data, then reporting a warning of
severity @code{:error} is the right way to inform the user of the
problem.  For instance, the Emacs Lisp byte compiler can report an
error that way and continue compiling other functions.  (If the
program signals a Lisp error and then handles it with
@code{condition-case}, the user won't see the error message; it could
show the message to the user by reporting it as a warning.)

@c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
@c "bytecomp" here?  The parens are part of warning-type-format but
@c not part of the warning type. --xfq
@cindex warning type
  Each warning has a @dfn{warning type} to classify it.  The type is a
list of symbols.  The first symbol should be the custom group that you
use for the program's user options.  For example, byte compiler
warnings use the warning type @code{(bytecomp)}.  You can also
subcategorize the warnings, if you wish, by using more symbols in the
list.

@defun display-warning type message &optional level buffer-name
This function reports a warning, using @var{message} as the message
and @var{type} as the warning type.  @var{level} should be the
severity level, with @code{:warning} being the default.

@var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
for logging the warning.  By default, it is @file{*Warnings*}.
@end defun

@defun lwarn type level message &rest args
This function reports a warning using the value of @code{(format
@var{message} @var{args}...)} as the message in the @file{*Warnings*}
buffer.  In other respects it is equivalent to @code{display-warning}.
@end defun

@defun warn message &rest args
This function reports a warning using the value of @code{(format
@var{message} @var{args}...)} as the message, @code{(emacs)} as the
type, and @code{:warning} as the severity level.  It exists for
compatibility only; we recommend not using it, because you should
specify a specific warning type.
@end defun

@node Warning Variables
@subsection Warning Variables
@cindex warning variables

  Programs can customize how their warnings appear by binding
the variables described in this section.

@defvar warning-levels
This list defines the meaning and severity order of the warning
severity levels.  Each element defines one severity level,
and they are arranged in order of decreasing severity.

Each element has the form @code{(@var{level} @var{string}
@var{function})}, where @var{level} is the severity level it defines.
@var{string} specifies the textual description of this level.
@var{string} should use @samp{%s} to specify where to put the warning
type information, or it can omit the @samp{%s} so as not to include
that information.

The optional @var{function}, if non-@code{nil}, is a function to call
with no arguments, to get the user's attention.

Normally you should not change the value of this variable.
@end defvar

@defvar warning-prefix-function
If non-@code{nil}, the value is a function to generate prefix text for
warnings.  Programs can bind the variable to a suitable function.
@code{display-warning} calls this function with the warnings buffer
current, and the function can insert text in it.  That text becomes
the beginning of the warning message.

The function is called with two arguments, the severity level and its
entry in @code{warning-levels}.  It should return a list to use as the
entry (this value need not be an actual member of
@code{warning-levels}).  By constructing this value, the function can
change the severity of the warning, or specify different handling for
a given severity level.

If the variable's value is @code{nil} then there is no function
to call.
@end defvar

@defvar warning-series
Programs can bind this variable to @code{t} to say that the next
warning should begin a series.  When several warnings form a series,
that means to leave point on the first warning of the series, rather
than keep moving it for each warning so that it appears on the last one.
The series ends when the local binding is unbound and
@code{warning-series} becomes @code{nil} again.

The value can also be a symbol with a function definition.  That is
equivalent to @code{t}, except that the next warning will also call
the function with no arguments with the warnings buffer current.  The
function can insert text which will serve as a header for the series
of warnings.

Once a series has begun, the value is a marker which points to the
buffer position in the warnings buffer of the start of the series.

The variable's normal value is @code{nil}, which means to handle
each warning separately.
@end defvar

@defvar warning-fill-prefix
When this variable is non-@code{nil}, it specifies a fill prefix to
use for filling each warning's text.
@end defvar

@defvar warning-type-format
This variable specifies the format for displaying the warning type
in the warning message.  The result of formatting the type this way
gets included in the message under the control of the string in the
entry in @code{warning-levels}.  The default value is @code{" (%s)"}.
If you bind it to @code{""} then the warning type won't appear at
all.
@end defvar

@node Warning Options
@subsection Warning Options
@cindex warning options

  These variables are used by users to control what happens
when a Lisp program reports a warning.

@defopt warning-minimum-level
This user option specifies the minimum severity level that should be
shown immediately to the user.  The default is @code{:warning}, which
means to immediately display all warnings except @code{:debug}
warnings.
@end defopt

@defopt warning-minimum-log-level
This user option specifies the minimum severity level that should be
logged in the warnings buffer.  The default is @code{:warning}, which
means to log all warnings except @code{:debug} warnings.
@end defopt

@defopt warning-suppress-types
This list specifies which warning types should not be displayed
immediately for the user.  Each element of the list should be a list
of symbols.  If its elements match the first elements in a warning
type, then that warning is not displayed immediately.
@end defopt

@defopt warning-suppress-log-types
This list specifies which warning types should not be logged in the
warnings buffer.  Each element of the list should be a list of
symbols.  If it matches the first few elements in a warning type, then
that warning is not logged.
@end defopt

@node Delayed Warnings
@subsection Delayed Warnings
@cindex delayed warnings

Sometimes, you may wish to avoid showing a warning while a command is
running, and only show it only after the end of the command.  You can
use the variable @code{delayed-warnings-list} for this.

@defvar delayed-warnings-list
The value of this variable is a list of warnings to be displayed after
the current command has finished.  Each element must be a list

@smallexample
(@var{type} @var{message} [@var{level} [@var{buffer-name}]])
@end smallexample

@noindent
with the same form, and the same meanings, as the argument list of
@code{display-warning} (@pxref{Warning Basics}).  Immediately after
running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
command loop displays all the warnings specified by this variable,
then resets it to @code{nil}.
@end defvar

  Programs which need to further customize the delayed warnings
mechanism can change the variable @code{delayed-warnings-hook}:

@defvar delayed-warnings-hook
This is a normal hook which is run by the Emacs command loop, after
@code{post-command-hook}, in order to to process and display delayed
warnings.

Its default value is a list of two functions:

@smallexample
(collapse-delayed-warnings display-delayed-warnings)
@end smallexample

@findex collapse-delayed-warnings
@findex display-delayed-warnings
@noindent
The function @code{collapse-delayed-warnings} removes repeated entries
from @code{delayed-warnings-list}.  The function
@code{display-delayed-warnings} calls @code{display-warning} on each
of the entries in @code{delayed-warnings-list}, in turn, and then sets
@code{delayed-warnings-list} to @code{nil}.
@end defvar

@node Invisible Text
@section 不可視なテキスト

@cindex 不可視なテキスト
属性@code{invisible}で文字群を@dfn{不可視}にできます。
つまり、それらをスクリーンに表示されないようにするのです。
この指定はテキスト属性（@pxref{Text Properties}）か
オーバレイの属性（@pxref{Overlays}）で使えます。
Cursor motion also partly ignores these
characters; if the command loop finds that point is inside a range of
invisible text after a command, it relocates point to the other side
of the text.

もっとも単純な場合、
属性@code{invisible}が@code{nil}以外であると文字は見えなくなります。
これはデフォルトの場合、つまり、
@code{buffer-invisibility-spec}のデフォルト値を変更していない場合であり、
このようにして属性@code{invisible}は動作します。
You should normally use @code{t}
as the value of the @code{invisible} property if you don't plan
to set @code{buffer-invisibility-spec} yourself.

より一般的には、変数@code{buffer-invisibility-spec}を使って、
属性@code{invisible}のどの値のものを不可視なテキストにするかを制御できます。
つまり、@code{invisible}の異なる値を与えて
テキストをあらかじめいくつかのグループに分類しておき、
そのあとで@code{buffer-invisibility-spec}の値を変更して
さまざまなグループを可視／不可視にします。

@code{buffer-invisibility-spec}で可視性を制御することは、
データベースの項目の一覧を表示するようなプログラムで特に有用です。
データベースの特定の項目だけを見るための
便利なフィルタコマンドを実装できます。
この変数に設定するのはとても速くでき、
変更すべき属性を探すためにバッファ内の全テキストを走査するよりも速いのです。

@defvar buffer-invisibility-spec
この変数は、属性@code{invisible}のどの種類を実際に
不可視な文字にするかを指定する。

@table @asis
@item @code{t}
属性@code{invisible}が@code{nil}以外の文字を不可視にする。
これがデフォルト。

@item リスト
リストの各要素で不可視にする条件を指定する。
文字の属性@code{invisible}がこれらの条件の1つを満たすと、
その文字を不可視にする。
リストには2種類の要素がありうる。

@table @code
@item @var{atom}
文字の属性@code{invisible}の値が@var{atom}であるか、
そのリストのメンバに@var{atom}があると、
文字を不可視にする。
比較は@code{eq}で行われる。

@item (@var{atom} . t)
文字の属性@code{invisible}の値が@var{atom}であるか、
そのリストのメンバに@var{atom}があると、
文字を不可視にする。比較は@code{eq}で行われる。
さらに、その文字が行末にあり、直後に目に見える改行がある場合には、
省略符号を表示する。
@end table
@end table
@end defvar

@code{buffer-invisibility-spec}に要素を追加したり削除するために
2つの関数が特別にあります。

@defun add-to-invisibility-spec element
この関数は、@code{buffer-invisibility-spec}に要素@var{element}を追加する。
If @code{buffer-invisibility-spec}
was @code{t}, it changes to a list, @code{(t)}, so that text whose
@code{invisible} property is @code{t} remains invisible.
@end defun

@defun remove-from-invisibility-spec element
@code{buffer-invisibility-spec}から要素@var{element}を削除する。
This does nothing if @var{element}
is not in the list.
@end defun

@code{buffer-invisibility-spec}の使い方の慣習の1つに、
メジャーモードでは
@code{buffer-invisibility-spec}の1要素と属性@code{invisible}の値に
モード自体の名前を使うべきであるというのがあります。

@example
;; @r{@samp{@dots{}}を表示したければ}
(add-to-invisibility-spec '(my-symbol . t)) 
;; @r{@samp{@dots{}}を表示しくなければ}
(add-to-invisibility-spec 'my-symbol) 

(overlay-put (make-overlay beginning end)
             'invisible 'my-symbol)

;; @r{オーバレイを終了したら}
(remove-from-invisibility-spec '(my-symbol . t))
;; @r{同じように}
(remove-from-invisibility-spec 'my-symbol)
@end example

  You can check for invisibility using the following function:

@defun invisible-p pos-or-prop
If @var{pos-or-prop} is a marker or number, this function returns a
non-@code{nil} value if the text at that position is invisible.

If @var{pos-or-prop} is any other kind of Lisp object, that is taken
to mean a possible value of the @code{invisible} text or overlay
property.  In that case, this function returns a non-@code{nil} value
if that value would cause text to become invisible, based on the
current value of @code{buffer-invisibility-spec}.
@end defun

@vindex line-move-ignore-invisible
普通、テキストを操作したりポイントを移動するコマンドは、
テキストの可視性に注意しません。
@code{next-line}や@code{previous-line}のような
ユーザーレベルの移動コマンドは、
@code{line-move-ignore-invisible}が@code{nil}（デフォルト値）以外であれば
不可視な改行を明示的に無視しますが、
それはそのように明示的にプログラムしてあるからにすぎません。

  If a command ends with point inside or at the boundary of
invisible text, the main editing loop relocates point to one of the
two ends of the invisible text.  Emacs chooses the direction of
relocation so that it is the same as the overall movement direction of
the command; if in doubt, it prefers a position where an inserted char
would not inherit the @code{invisible} property.  Additionally, if the
text is not replaced by an ellipsis and the command only moved within
the invisible text, then point is moved one extra character so as to
try and reflect the command's movement by a visible movement of the
cursor.

  Thus, if the command moved point back to an invisible range (with the usual
stickiness), Emacs moves point back to the beginning of that range.  If the
command moved point forward into an invisible range, Emacs moves point forward
to the first visible character that follows the invisible text and then forward
one more character.

  These @dfn{adjustments} of point that ended up in the middle of
invisible text can be disabled by setting @code{disable-point-adjustment}
to a non-@code{nil} value.  @xref{Adjusting Point}.

インクリメンタルサーチでは、
不可視なテキストを含む一致箇所では、
不可視なオーバレイを一時的にあるいは恒久的に可視にできます。
これを可能にするには、オーバレイの属性@code{isearch-open-invisible}が
@code{nil}以外である必要があります。
その属性の値は、オーバレイを引数として呼ばれる関数である必要があります。
その関数がオーバレイを恒久的に可視にします。
その関数は、探索から抜けるときに一致箇所が
オーバレイにまたがっているときに使われます。

探索中には、そのようなオーバレイは、
それらの不可視・不可触属性を一時的に変更することで
一時的に可視にされます。
特定のオーバレイに対して異なる扱いをしたければ、
属性@code{isearch-open-invisible-temporary}に関数を与えておきます。
その関数は2つの引数で呼ばれます。
第1引数はオーバレイ、
第2引数は、オーバレイを可視にする@code{t}、あるいは、
オーバレイを再度不可視にする@code{nil}です。

@node Selective Display
@section 選択表示
@c @cindex selective display   Duplicates selective-display

@dfn{選択表示}とは、
スクリーン上の特定の行を隠すための関連する機能対を指します。

@cindex 明示的な選択表示
最初の変種は、明示的な選択表示で、
Lispプログラムで使用するために設計されています。
テキストを変更することでどの行を隠すかを制御します。
この種の隠蔽は現在は使われません。
その代わりに、@code{invisible}属性（@pxref{Invisible Text}）で、
同じ効果を得られます。

2番目の変種は、字下げに基づいて自動的に隠す行を選択します。
この変種は、ユーザーレベルの機能であるように設計されています。

明示的な選択表示を制御するには、
改行（コントロールJ）を復帰（コントロールM）に置き換えます。
置換前の改行に続いていたそれまでの行は見えなくなります。
厳密にいえば、改行だけが行を区切るため、
一時的にはもう行ではなくなっているのです。
つまり、先行する行の一部になっているのです。

選択表示は、編集コマンドに直接には影響しません。
たとえば、@kbd{C-f}（@code{forward-char}）は
躊躇なく不可視なテキストの中へポイントを移動します。
しかし、改行文字を復帰文字に置換すると
影響を受ける編集コマンドもあります。
たとえば、@code{next-line}は、
改行だけを探すため不可視な行を飛び越してしまいます。
選択表示を使用するモードでは、
改行を考慮するようにコマンドを定義したり、
テキストの一部を可視／不可視にするコマンドを定義できます。

選択表示しているバッファをファイルに書き出すときには、
すべてのコントロールM（復帰）は改行として出力されます。
つまり、つぎにファイルを読み込むと不可視なものはなく、
普通に見えるのです。
選択表示の効果は、Emacsの内側だけで見えるのです。

@defvar selective-display
このバッファローカルな変数は、選択表示をオンにする。
つまり、行や行の一部を不可視にできる。

@itemize @bullet
@item
@code{selective-display}の値が@code{t}であると、
行内のコントロールM（復帰）以降の部分を表示しない。
これは明示的な選択表示である。

@item
@code{selective-display}の値が正整数であると、
字下げのコラム幅がその数より大きな行を表示しない。
@end itemize

バッファのある部分が不可視であると、
垂直方向に移動するコマンドは、
その部分が存在しないがごとく動作し、
1つのコマンド@code{next-line}で任意個数の不可視行を飛び越えられる。
しかし、（@code{forward-char}などの）
文字単位の移動コマンドは不可視な部分を無視せず、
不可視な部分へのテキストの挿入／削除は可能である。

つぎの例では、@code{selective-display}の値を変えて
バッファ@code{foo}の@emph{見た目}を示す。
バッファの@emph{内容}に変更はない。

@example
@group
(setq selective-display nil)
     @result{} nil

---------- Buffer: foo ----------
1 on this column
 2on this column
  3n this column
  3n this column
 2on this column
1 on this column
---------- Buffer: foo ----------
@end group

@group
(setq selective-display 2)
     @result{} 2

---------- Buffer: foo ----------
1 on this column
 2on this column
 2on this column
1 on this column
---------- Buffer: foo ----------
@end group
@end example
@end defvar

@defopt selective-display-ellipses
このバッファローカルな変数が@code{nil}以外であると、
不可視なテキストが続く行末に@samp{@dots{}}を表示する。
つぎの例は、上の例の続きである。

@example
@group
(setq selective-display-ellipses t)
     @result{} t

---------- Buffer: foo ----------
1 on this column
 2on this column ...
 2on this column
1 on this column
---------- Bufferc: foo ----------
@end group
@end example

表示テーブルを使って@samp{@dots{}}にかわる別のテキストを指定できる。
@xref{Display Tables}。
@end defopt

@node Temporary Displays
@section Temporary Displays
@cindex temporary display
@cindex temporary buffer display

  Temporary displays are used by Lisp programs to put output into a
buffer and then present it to the user for perusal rather than for
editing.  Many help commands use this feature.

@defmac with-output-to-temp-buffer buffer-name body@dots{}
この関数は、@var{buffer-name}という名前のバッファに
本体@var{body}の任意の出力が挿入されるように準備したあとで
本体を実行する。
このバッファは必要に応じて最初に生成され、Helpモードに設定される。
（後述の類似関数@code{with-temp-buffer-window}を参照。）
最後に、適当なウィンドウに表示されるが、
そのウィンドウは選択されない。

If the forms in @var{body} do not change the major mode in the output
buffer, so that it is still Help mode at the end of their execution,
then @code{with-output-to-temp-buffer} makes this buffer read-only at
the end, and also scans it for function and variable names to make them
into clickable cross-references.  @xref{Docstring hyperlinks, , Tips for
Documentation Strings}, in particular the item on hyperlinks in
documentation strings, for more details.

文字列@var{buffer-name}は、既存である必要はない一時的なバッファを指定する。
引数は、バッファではなく文字列であること。
（問い合わせずに）はじめにバッファを消去し、
@code{with-output-to-temp-buffer}が終了すると未変更と印を付ける。

@code{with-output-to-temp-buffer}は、
@code{standard-output}に一時的なバッファを束縛し、
@var{body}のフォーム群を評価する。
@var{body}内で用いたLisp出力関数からの出力は
デフォルトでそのバッファに入る
（しかし、スクリーン表示やエコー領域のメッセージは、
用語の一般的な意味で『出力』であるが、
影響されない。）
@xref{Output Functions}。

Several hooks are available for customizing the behavior
of this construct; they are listed below.

@var{body}の最後のフォームの値を返す。

@example
@group
---------- Buffer: foo ----------
 This is the contents of foo.
---------- Buffer: foo ----------
@end group

@group
(with-output-to-temp-buffer "foo"
    (print 20)
    (print standard-output))
@result{} #<buffer foo>

---------- Buffer: foo ----------

20

#<buffer foo>

---------- Buffer: foo ----------
@end group
@end example
@end defmac

@defopt temp-buffer-show-function
この変数が@code{nil}以外ならば、
ヘルプバッファを表示するために
@code{with-output-to-temp-buffer}がこの値を関数として呼び出す。
関数は1つの引数、つまり、表示すべきバッファを受け取る。

この関数では、
@code{save-selected-window}を使いウィンドウとバッファを選択した内側で、
@code{with-output-to-temp-buffer}が普通に行うように
@code{temp-buffer-show-hook}を呼び出すのがよい。
@end defopt

@defvar temp-buffer-setup-hook
This normal hook is run by @code{with-output-to-temp-buffer} before
evaluating @var{body}.  When the hook runs, the temporary buffer is
current.  This hook is normally set up with a function to put the
buffer in Help mode.
@end defvar

@defvar temp-buffer-show-hook
このノーマルフックは、ヘルプバッファを表示後に
@code{with-output-to-temp-buffer}が実行する。
フックを実行するときには、
ヘルプバッファがカレントバッファであり、
それを表示しているウィンドウが選択されているウィンドウである。
@end defvar

@defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
This macro is similar to @code{with-output-to-temp-buffer}.  Like that
construct, it executes @var{body} while arranging to insert any output
it prints into the buffer named @var{buffer-or-name} and displays that
buffer in some window.  Unlike @code{with-output-to-temp-buffer},
however, it does not automatically switch that buffer to Help mode.

The argument @var{buffer-or-name} specifies the temporary buffer.  It
can be either a buffer, which must already exist, or a string, in which
case a buffer of that name is created, if necessary.  The buffer is
marked as unmodified and read-only when @code{with-temp-buffer-window}
exits.

This macro does not call @code{temp-buffer-show-function}.  Rather, it
passes the @var{action} argument to @code{display-buffer}
(@pxref{Choosing Window}) in order to display the buffer.

The value of the last form in @var{body} is returned, unless the
argument @var{quit-function} is specified.  In that case, it is called
with two arguments: the window showing the buffer and the result of
@var{body}.  The final return value is then whatever @var{quit-function}
returns.

@vindex temp-buffer-window-setup-hook
@vindex temp-buffer-window-show-hook
This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
and @code{temp-buffer-window-show-hook} in place of the analogous hooks
run by @code{with-output-to-temp-buffer}.
@end defmac

The two constructs described next are mostly identical to
@code{with-temp-buffer-window} but differ from it as specified:

@defmac with-current-buffer-window buffer-or-name action quit-function &rest body
This macro is like @code{with-temp-buffer-window} but unlike that makes
the buffer specified by @var{buffer-or-name} current for running
@var{body}.
@end defmac

@defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
This macro is like @code{with-current-buffer-window} but unlike that
displays the buffer specified by @var{buffer-or-name} @emph{before}
running @var{body}.
@end defmac

A window showing a temporary buffer can be fit to the size of that
buffer using the following mode:

@defopt temp-buffer-resize-mode
When this minor mode is enabled, windows showing a temporary buffer are
automatically resized to fit their buffer's contents.

A window is resized if and only if it has been specially created for the
buffer.  In particular, windows that have shown another buffer before
are not resized.  By default, this mode uses @code{fit-window-to-buffer}
(@pxref{Resizing Windows}) for resizing.  You can specify a different
function by customizing the options @code{temp-buffer-max-height} and
@code{temp-buffer-max-width} below.
@end defopt

@defopt temp-buffer-max-height
This option specifies the maximum height (in lines) of a window
displaying a temporary buffer when @code{temp-buffer-resize-mode} is
enabled.  It can also be a function to be called to choose the height
for such a buffer.  It gets one argument, the buffer, and should return
a positive integer.  At the time the function is called, the window to
be resized is selected.
@end defopt

@defopt temp-buffer-max-width
This option specifies the maximum width of a window (in columns)
displaying a temporary buffer when @code{temp-buffer-resize-mode} is
enabled.  It can also be a function to be called to choose the width for
such a buffer.  It gets one argument, the buffer, and should return a
positive integer.  At the time the function is called, the window to be
resized is selected.
@end defopt

The following function uses the current buffer for temporal display:

@defun momentary-string-display string position &optional char message
この関数は、カレントバッファ内の位置@var{position}に
文字列@var{string}を瞬間的に表示する。
アンドゥリストやバッファの変更状態には影響しない。

瞬間的な表示は、つぎの入力イベントまで持続する。
つぎの入力イベントが@var{char}であると、
@code{momentary-string-display}はそれを無視して戻る。
さもなければ、そのイベントは入力として使われるように保存される。
したがって、@var{char}を打つと文字列の表示が単に消えるだけであるが、
（たとえば）@kbd{C-f}を打つと文字列の表示が消えるだけでなく
（たぶん）ポイントを進めることになる。
引数@var{char}はデフォルトでは空白である。

@code{momentary-string-display}の戻り値に意味はない。

文字列@var{string}にコントロール文字が含まれなければ、
属性@code{before-string}のオーバレイを作成（のちに削除）することで
より一般的な方法で同じことを行える。
@xref{Overlay Properties}。

@var{message}が@code{nil}以外ならば、
@var{string}をバッファに表示されている間、
エコー領域に表示される。
@code{nil}ならば、デフォルトは
「継続するには文字@var{char}を打つこと」
といったメッセージである。

つぎの例では、ポイントは始めは2行目の先頭に位置している。

@example
@group
---------- Buffer: foo ----------
This is the contents of foo.
@point{}Second line.
---------- Buffer: foo ----------
@end group

@group
(momentary-string-display
  "**** Important Message! ****"
  (point) ?\r
  "Type RET when done reading")
@result{} t
@end group

@group
---------- Buffer: foo ----------
This is the contents of foo.
**** Important Message! ****Second line.
---------- Buffer: foo ----------

---------- Echo Area ----------
Type RET when done reading
---------- Echo Area ----------
@end group
@end example
@end defun

@node Overlays
@section オーバレイ
@cindex オーバレイ
@c FIXME: mention intervals in this section?

ユーザーに提示するためにスクリーン上でのバッファのテキストの見た目を
変えるために@dfn{オーバレイ}（overlay）を使えます。
オーバレイは、特定のバッファに属するオブジェクトであり、
指定された開始位置と終了位置があります。
また、調べたり設定できる属性もあります。
これらの属性は、オーバレイの内側のテキストの表示に影響します。

@cindex scalability of overlays
@cindex overlays, scalability
The visual effect of an overlay is the same as of the corresponding
text property (@pxref{Text Properties}).  However, due to a different
implementation, overlays generally don't scale well (many operations
take a time that is proportional to the number of overlays in the
buffer).  If you need to affect the visual appearance of many portions
in the buffer, we recommend using text properties.

An overlay uses markers to record its beginning and end; thus,
editing the text of the buffer adjusts the beginning and end of each
overlay so that it stays with the text.  When you create the overlay,
you can specify whether text inserted at the beginning should be
inside the overlay or outside, and likewise for the end of the overlay.

@menu
* Managing Overlays::   Creating and moving overlays.
* Overlay Properties::  How to read and set properties.
                          What properties do to the screen display.
* Finding Overlays::    Searching for overlays.
@end menu

@node Managing Overlays
@subsection オーバレイの管理
@cindex managing overlays
@cindex overlays, managing

本節では、オーバレイを作成、削除、移動したり、
それらの内容を調べる関数について述べます。
Overlay changes are not
recorded in the buffer's undo list, since the overlays are not
part of the buffer's contents.

@defun overlayp object
This function returns @code{t} if @var{object} is an overlay.
@end defun

@defun make-overlay start end &optional buffer front-advance rear-advance
この関数は、バッファ@var{buffer}に属する
@var{start}から@var{end}までを覆うオーバレイを作成しそれを返す。
@var{start}と@var{end}のどちらもバッファ内位置を指定する
整数かマーカであること。
@var{buffer}を省略すると、カレントバッファにオーバレイを作成する。

@cindex empty overlay
@cindex overlay, empty
An overlay whose @var{start} and @var{end} specify the same buffer
position is known as @dfn{empty}.  A non-empty overlay can become
empty if the text between its @var{start} and @var{end} is deleted.
When that happens, the overlay is by default not deleted, but you can
cause it to be deleted by giving it the @samp{evaporate} property
(@pxref{Overlay Properties, evaporate property}).

引数@var{front-advance}と@var{rear-advance}は、それぞれ
オーバレイの開始位置と終了位置における挿入型を指定する。
@xref{Marker Insertion Types}。
If they
are both @code{nil}, the default, then the overlay extends to include
any text inserted at the beginning, but not text inserted at the end.
If @var{front-advance} is non-@code{nil}, text inserted at the
beginning of the overlay is excluded from the overlay.  If
@var{rear-advance} is non-@code{nil}, text inserted at the end of the
overlay is included in the overlay.
@end defun

@defun overlay-start overlay
この関数は、オーバレイ@var{overlay}の開始位置を整数で返す。
@end defun

@defun overlay-end overlay
この関数は、オーバレイ@var{overlay}の終了位置を整数で返す。
@end defun

@defun overlay-buffer overlay
この関数は、オーバレイ@var{overlay}が属するバッファを返す。
It returns @code{nil} if @var{overlay} has been deleted.
@end defun

@defun delete-overlay overlay
この関数は、オーバレイ@var{overlay}を削除する。
Lispオブジェクトとしてはオーバレイは存在し続けるが、
それが属したバッファとの対応付けは消失し、
表示上の効果もなくなる。

削除したオーバレイは恒久的に無意味ではない。
@code{move-overlay}を呼び出して新たなバッファ内位置をそれに与えられる。
@end defun

@defun move-overlay overlay start end &optional buffer
この関数は、オーバレイ@var{overlay}をバッファ@var{buffer}に移し、
@var{start}から@var{end}を覆うようにする。
@var{start}と@var{end}のどちらもバッファ内位置を指定し、
整数かマーカである。

@var{buffer}を省略すると、@var{overlay}は同じバッファに留まる。
@var{overlay}が削除されると、現在のバッファに行く。

戻り値は@var{overlay}である。

これは、オーバレイの端を変更する唯一の正しい方法である。
オーバレイのマーカを手で修正しようとしないこと。
他の重要なデータ構造を更新しそこない、
いくつかのオーバレイを『失う』ことにもなりかねない。
@end defun

@defun remove-overlays &optional start end name value
This function removes all the overlays between @var{start} and
@var{end} whose property @var{name} has the value @var{value}.  It can
move the endpoints of the overlays in the region, or split them.

If @var{name} is omitted or @code{nil}, it means to delete all overlays in
the specified region.  If @var{start} and/or @var{end} are omitted or
@code{nil}, that means the beginning and end of the buffer respectively.
Therefore, @code{(remove-overlays)} removes all the overlays in the
current buffer.
@end defun

@defun copy-overlay overlay
This function returns a copy of @var{overlay}.  The copy has the same
endpoints and properties as @var{overlay}.  However, the marker
insertion type for the start of the overlay and for the end of the
overlay are set to their default values (@pxref{Marker Insertion
Types}).
@end defun

  Here are some examples:

@example
;; @r{Create an overlay.}
(setq foo (make-overlay 1 10))
     @result{} #<overlay from 1 to 10 in display.texi>
(overlay-start foo)
     @result{} 1
(overlay-end foo)
     @result{} 10
(overlay-buffer foo)
     @result{} #<buffer display.texi>
;; @r{Give it a property we can check later.}
(overlay-put foo 'happy t)
     @result{} t
;; @r{Verify the property is present.}
(overlay-get foo 'happy)
     @result{} t
;; @r{Move the overlay.}
(move-overlay foo 5 20)
     @result{} #<overlay from 5 to 20 in display.texi>
(overlay-start foo)
     @result{} 5
(overlay-end foo)
     @result{} 20
;; @r{Delete the overlay.}
(delete-overlay foo)
     @result{} nil
;; @r{Verify it is deleted.}
foo
     @result{} #<overlay in no buffer>
;; @r{A deleted overlay has no position.}
(overlay-start foo)
     @result{} nil
(overlay-end foo)
     @result{} nil
(overlay-buffer foo)
     @result{} nil
;; @r{Undelete the overlay.}
(move-overlay foo 1 20)
     @result{} #<overlay from 1 to 20 in display.texi>
;; @r{Verify the results.}
(overlay-start foo)
     @result{} 1
(overlay-end foo)
     @result{} 20
(overlay-buffer foo)
     @result{} #<buffer display.texi>
;; @r{Moving and deleting the overlay does not change its properties.}
(overlay-get foo 'happy)
     @result{} t
@end example

  Emacs stores the overlays of each buffer in two lists, divided
around an arbitrary ``center position''.  One list extends backwards
through the buffer from that center position, and the other extends
forwards from that center position.  The center position can be anywhere
in the buffer.

@defun overlay-recenter pos
This function recenters the overlays of the current buffer around
position @var{pos}.  That makes overlay lookup faster for positions
near @var{pos}, but slower for positions far away from @var{pos}.
@end defun

  A loop that scans the buffer forwards, creating overlays, can run
faster if you do @code{(overlay-recenter (point-max))} first.

@node Overlay Properties
@subsection オーバレイ属性
@cindex オーバレイ属性

オーバレイ属性はある意味でテキスト属性に似ていて、
どちらの属性でも文字の表示方法を変更できます。
しかし、多くの点で異なります。
比較のために@xref{Text Properties}。

テキスト属性は、テキストの一部であるとみなされますが、
オーバレイはテキストの一部とはみなしません。
したがって、さまざまなバッファや文字列のあいだでテキストをコピーしても
テキスト属性は保存されますが、オーバレイは保存されません。
バッファ内のテキスト属性を変更するとバッファを変更済みと印を付けますが、
オーバレイを移動したりその属性を変更しても
バッファの変更とは考えません。
テキスト属性の変更と異なり、
オーバレイの変更はバッファのアンドゥリストには記録されません。

  Since more than one overlay can specify a property value for the
same character, Emacs lets you specify a priority value of each
overlay.  In case two overlays have the same priority value, and one
is nested in the other, then the inner one will have priority over the
outer one.  If neither is nested in the other then you should not make
assumptions about which overlay will prevail.

  These functions read and set the properties of an overlay:

@defun overlay-get overlay prop
この関数は、オーバレイ@var{overlay}に記録されている
属性@var{prop}の値をあれば返す。
@var{overlay}にそのような属性に対する値が記録されていなくても、
属性@code{category}がありそれがシンボルであれば、
そのシンボルの属性@var{prop}を使う。
さもなければ値は@code{nil}である。
@end defun

@defun overlay-put overlay prop value
この関数は、オーバレイ@var{overlay}に属性@var{prop}の値として
@var{value}を設定する。
@var{value}を返す。
@end defun

@defun overlay-properties overlay
This returns a copy of the property list of @var{overlay}.
@end defun

与えられた文字のオーバレイ属性とテキスト属性の両方を調べる
関数@code{get-char-property}も参照してください。
@xref{Examining Properties}。

  Many overlay properties have special meanings; here is a table
of them:

@table @code
@item priority
@kindex priority @r{（オーバレイ属性）}
この属性の値は、オーバレイの優先順位を決定する。
優先順位の指定には、@code{nil}または０以上の整数値を指定する。
それ以外の値の場合は、動作は未定義である。

優先順位は、複数のオーバレイが同じ文字を覆い、
いずれも表示用のフェイスを指定している場合に意味を持つ。
@code{priority}の大きなものが他に優先する。
@code{face}属性については、より高い優先度のものが完全に
他の値をオーバーライドしない。その代わりに、フェイス属性は
より低い優先度の@code{face}属性をオーバーライドする。

現在、すべてのオーバレイ属性はテキスト属性に優先する。

Note that Emacs sometimes uses non-numeric priority values for some of
its internal overlays, so do not try to do arithmetic on the
priority of an overlay (unless it is one that you created).  If you
need to put overlays in priority order, use the @var{sorted} argument
of @code{overlays-at}.  @xref{Finding Overlays}.

@item window
@kindex window @r{（オーバレイ属性）}
属性@code{window}が@code{nil}以外であると、
オーバレイをそのウィンドウだけに適用する。

@item category
@kindex category @r{（オーバレイ属性）}
オーバレイに属性@code{category}があると、
それをオーバレイの@dfn{カテゴリ}（category）と呼ぶ。
これはシンボルであること。
シンボルの属性がオーバレイの属性のデフォルトの役割を果たす。

@item face
@kindex face @r{（オーバレイ属性）}
この属性は、テキストの表示方法を制御する（@pxref{Faces}）。
属性の値には、以下の様なものが有る。

@itemize @bullet
@item
A face name (a symbol or string).

@item
An anonymous face: a property list of the form @code{(@var{keyword}
@var{value} @dots{})}, where each @var{keyword} is a face attribute
name and @var{value} is a value for that attribute.

@item
A list of faces.  Each list element should be either a face name or an
anonymous face.  This specifies a face which is an aggregate of the
attributes of each of the listed faces.  Faces occurring earlier in
the list have higher priority.

@item
@code{(foreground-color . @var{color-name})}か
@code{(background-color . @var{color-name})}の consセル。
これは、@code{(:foreground
@var{color-name})}や@code{(:background @var{color-name})}
のように前景色だけや背景色を指定する。
この形式は過去との互換性のためだけにサポートされており、
使用すべきではない。
@end itemize

@item mouse-face
@kindex mouse-face @r{（オーバレイ属性）}
この属性は、マウスがオーバレイの範囲に入っているときに
@code{face}のかわりに使われる。
However, Emacs ignores all face attributes
from this property that alter the text size (e.g., @code{:height},
@code{:weight}, and @code{:slant}).  Those attributes are always the
same as in the unhighlighted text.

@item display
@kindex display @r{(overlay property)}
This property activates various features that change the
way text is displayed.  For example, it can make text appear taller
or shorter, higher or lower, wider or narrower, or replaced with an image.
@xref{Display Property}.

@item help-echo
@kindex help-echo @r{(overlay property)}
If an overlay has a @code{help-echo} property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window.  For details see @ref{Text
help-echo}.

@item field
@kindex field @r{(overlay property)}
@c Copied from Special Properties.
Consecutive characters with the same @code{field} property constitute a
@emph{field}.  Some motion functions including @code{forward-word} and
@code{beginning-of-line} stop moving at a field boundary.
@xref{Fields}.

@item modification-hooks
@kindex modification-hooks @r{（オーバレイ属性）}
この属性の値は、オーバレイの内側の文字を変更したり、
オーバレイの内側にテキストを挿入したときに
呼び出される関数のリストである。

フック関数は、各変更の前後に呼び出される。
関数が受け取った情報を保存し呼び出しごとに比較すれば
バッファテキストにどのような変更が行われたかを正確に判定できる。

変更前に呼ばれるときには、各関数は4つの引数を受け取る。
オーバレイ、@code{nil}、変更対象のテキスト範囲の先頭と末尾である。

変更後に呼ばれるときには、各関数は5つの引数を受け取る。
オーバレイ、@code{t}、変更済みのテキスト範囲の先頭と末尾、
その範囲の変更前のテキストの長さである。
（挿入では変更前の長さはゼロである。
削除では変更前の長さは削除された文字数であり、
変更後の先頭位置と末尾位置は同じである。）

If these functions modify the buffer, they should bind
@code{inhibit-modification-hooks} to @code{t} around doing so, to
avoid confusing the internal mechanism that calls these hooks.

Text properties also support the @code{modification-hooks} property,
but the details are somewhat different (@pxref{Special Properties}).

@item insert-in-front-hooks
@kindex insert-in-front-hooks @r{（オーバレイ属性）}
この属性の値は、オーバレイの開始位置へのテキスト挿入の前後に
呼び出される関数のリストである。
呼び出し方法は@code{modification-hooks}の関数群と同じである。

@item insert-behind-hooks
@kindex insert-behind-hooks @r{（オーバレイ属性）}
この属性の値は、オーバレイの終了位置へのテキスト挿入の前後に
呼び出される関数のリストである。
呼び出し方法は@code{modification-hooks}の関数群と同じである。

@item invisible
@kindex invisible @r{（オーバレイ属性）}
属性@code{invisible}は、オーバレイ内のテキストを不可視にする。
つまり、それらはスクリーン上に現れない。
詳しくは、@xref{Invisible Text}。

@item intangible
@kindex intangible @r{（オーバレイ属性）}
属性@code{intangible}は、オーバレイにおいて
テキスト属性@code{intangible}と同様に働く。
詳しくは、@xref{Special Properties}。

@item isearch-open-invisible
この属性は、インクリメンタルサーチに対して、
一致箇所がオーバレイに重なったときに
不可視なオーバレイを恒久的に可視にする方法を指示する。
@xref{Invisible Text}。

@item isearch-open-invisible-temporary
この属性は、インクリメンタルサーチに対して、
探索中に不可視なオーバレイを一時的に可視にする方法を指示する。
@xref{Invisible Text}。

@item before-string
@kindex before-string @r{（オーバレイ属性）}
This property's value is a string to add to the display at the beginning
of the overlay.  The string does not appear in the buffer in any
sense---only on the screen.
この属性の値は、オーバレイの先頭位置に追加表示する文字列である。
文字列はいかなる意味においてもバッファには現れず、
スクリーン上のみに現れる。
文字列は1コラムで表示される文字のみであること。
タブや改行を含むコントロール文字を含むと奇妙な結果を生じる。

@item after-string
@kindex after-string @r{（オーバレイ属性）}
この属性の値は、オーバレイの末尾位置に追加表示する文字列である。
文字列はいかなる意味においてもバッファには現れず、
スクリーン上のみに現れる。

@item line-prefix
This property specifies a display spec to prepend to each
non-continuation line at display-time.  @xref{Truncation}.

@item wrap-prefix
This property specifies a display spec to prepend to each continuation
line at display-time.  @xref{Truncation}.

@item evaporate
@kindex evaporate @r{（オーバレイ属性）}
この属性が@code{nil}以外であると、
オーバレイが空に（つまり覆う文字がなく）なると、
自動的にオーバレイを削除する。
If you give
an empty overlay (@pxref{Managing Overlays, empty overlay}) a
non-@code{nil} @code{evaporate} property, that deletes it immediately.
Note that, unless an overlay has this property, it will not be deleted
when the text between its starting and ending positions is deleted
from the buffer.

@item keymap
@cindex keymap of character (and overlays)
@kindex keymap @r{(overlay property)}
If this property is non-@code{nil}, it specifies a keymap for a portion of the
text.  This keymap is used when the character after point is within the
overlay, and takes precedence over most other keymaps.  @xref{Active Keymaps}.

@item local-map
@kindex local-map @r{(overlay property)}
@code{local-map}属性は@code{keymap}と似ているが、
既存のキーマップを強化するのではなく、
バッファローカルなキーマップを置き換える。
This also means it has lower precedence than minor mode keymaps.
@end table

The @code{keymap} and @code{local-map} properties do not affect a
string displayed by the @code{before-string}, @code{after-string}, or
@code{display} properties.  This is only relevant for mouse clicks and
other mouse events that fall on the string, since point is never on
the string.  To bind special mouse events for the string, assign it a
@code{keymap} or @code{local-map} text property.  @xref{Special
Properties}.

@node Finding Overlays
@subsection Searching for Overlays
@cindex searching for overlays
@cindex overlays, searching for

@defun overlays-at pos &optional sorted
この関数は、カレントバッファの位置@var{pos}を覆うすべての
オーバレイのリストを返す。
If @var{sorted} is non-@code{nil},
the list is in decreasing order of priority, otherwise このリスト内の順番に意味はない。
オーバレイが位置@var{pos}かそのまえで始まり、かつ、
位置@var{pos}かそのうしろで終るときに、
オーバレイは位置@var{pos}を覆う。

To illustrate usage, here is a Lisp function that returns a list of the
overlays that specify property @var{prop} for the character at point:

@smallexample
(defun find-overlays-specifying (prop)
  (let ((overlays (overlays-at (point)))
        found)
    (while overlays
      (let ((overlay (car overlays)))
        (if (overlay-get overlay prop)
            (setq found (cons overlay found))))
      (setq overlays (cdr overlays)))
    found))
@end smallexample
@end defun

@defun overlays-in beg end
この関数は、@var{beg}から@var{end}までの領域と
重なり合っているすべてのオーバレイのリストを返す。
『重なり合っている』とは、
少なくとも1文字がオーバレイに覆われていて、かつ、
その文字が指定された領域に入っていることを意味する。
しかし、空のオーバレイ（@pxref{Managing Overlays,
empty overlay}）であっても
それが@var{beg}にあるか、または@var{beg}と@var{end}の間にあるか、
または@var{end}がバッファの最後を示すときの@var{end}にある場合は、
結果に含まれる。
@end defun

@defun next-overlay-change pos
この関数は、位置@var{pos}のうしろにある
オーバレイのつぎの開始位置か終了位置を返す。
If there is none, it returns @code{(point-max)}.
@end defun

@defun previous-overlay-change pos
この関数は、位置@var{pos}のまえにある
オーバレイのまえの開始位置か終了位置を返す。
If there is none, it returns @code{(point-min)}.
@end defun

  As an example, here's a simplified (and inefficient) version of the
primitive function @code{next-single-char-property-change}
(@pxref{Property Search}).  It searches forward from position
@var{pos} for the next position where the value of a given property
@code{prop}, as obtained from either overlays or text properties,
changes.

@smallexample
(defun next-single-char-property-change (position prop)
  (save-excursion
    (goto-char position)
    (let ((propval (get-char-property (point) prop)))
      (while (and (not (eobp))
                  (eq (get-char-property (point) prop) propval))
        (goto-char (min (next-overlay-change (point))
                        (next-single-property-change (point) prop)))))
    (point)))
@end smallexample

@node Size of Displayed Text
@section Size of Displayed Text
@cindex size of text on display
@cindex character width on display

すべての文字が同じ表示幅ではないため、
これらの関数を使って文字の表示幅を調べることができる。
関連する関数については、@xref{Primitive Indent}と@ref{Screen Lines}。

@defun char-width char
この関数は、文字@var{char}を
カレントバッファに表示した場合のコラム幅を返す。
(i.e., taking
into account the buffer's display table, if any; @pxref{Display
Tables}).  The width of a tab character is usually @code{tab-width}
(@pxref{Usual Display}).
@end defun

@defun string-width string
この関数は、文字列@var{string}を選択されているウィンドウで
カレントバッファに表示した場合のコラム幅を返す。
@end defun

@defun truncate-string-to-width string width &optional start-column padding ellipsis
この関数は、幅@var{width}に収まる文字列@var{string}の部分を
新たな文字列として返す。

@var{string}が幅@var{width}に満たない場合、
@var{string}の終りで結果は終る。
@var{string}内の1つの複数コラム文字がコラム@var{width}を越える場合には、
その文字は結果に含めない。
したがって、結果は@var{width}より短くなりえるがそれを越えることはない。

省略可能な引数@var{start-column}は、開始コラムを指定する。
これが@code{nil}以外であると、文字列のはじめの
@var{start-column}コラムを結果から省く。
@var{string}内の1つの複数コラム文字がコラム@var{start-column}を越える場合には、
その文字は結果に含めない。

省略可能な引数@var{padding}が@code{nil}以外であると、
結果の文字列の先頭や末尾に付加して
ちょうど@var{width}コラムにするためのパディング文字である。
@var{width}より短くなる場合に
結果の末尾にパディング文字を使う。
@var{string}の複数コラム文字がコラム@var{start-column}を越える場合には、
結果の先頭にパディング文字を使う。

If @var{ellipsis} is non-@code{nil}, it should be a string which will
replace the end of @var{string} (including any padding) if it extends
beyond @var{width}, unless the display width of @var{string} is equal
to or less than the display width of @var{ellipsis}.  If
@var{ellipsis} is non-@code{nil} and not a string, it stands for
@code{"..."}.

@example
(truncate-string-to-width "\tab\t" 12 4)
     @result{} "ab"
(truncate-string-to-width "\tab\t" 12 4 ?\s)
     @result{} "    ab  "
@end example
@end defun

The following function returns the size in pixels of text as if it were
displayed in a given window.  This function is used by
@code{fit-window-to-buffer} (@pxref{Resizing Windows}) and
@code{fit-frame-to-buffer} (@pxref{Size and Position}) to make a window
exactly as large as the text it contains.

@defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
This function returns the size of the text of @var{window}'s buffer in
pixels.  @var{window} must be a live window and defaults to the selected
one.  The return value is a cons of the maximum pixel-width of any text
line and the maximum pixel-height of all text lines.

The optional argument @var{from}, if non-@code{nil}, specifies the first
text position to consider and defaults to the minimum accessible
position of the buffer.  If @var{from} is @code{t}, it uses the minimum
accessible position that is not a newline character.  The optional
argument @var{to}, if non-@code{nil}, specifies the last text position
to consider and defaults to the maximum accessible position of the
buffer.  If @var{to} is @code{t}, it uses the maximum accessible
position that is not a newline character.

The optional argument @var{x-limit}, if non-@code{nil}, specifies the
maximum pixel-width that can be returned.  @var{x-limit} @code{nil} or
omitted, means to use the pixel-width of @var{window}'s body
(@pxref{Window Sizes}); this is useful when the caller does not intend
to change the width of @var{window}.  Otherwise, the caller should
specify here the maximum width @var{window}'s body may assume.  Text
whose x-coordinate is beyond @var{x-limit} is ignored.  Since
calculating the width of long lines can take some time, it's always a
good idea to make this argument as small as needed; in particular, if
the buffer might contain long lines that will be truncated anyway.

The optional argument @var{y-limit}, if non-@code{nil}, specifies the
maximum pixel-height that can be returned.  Text lines whose
y-coordinate is beyond @var{y-limit} are ignored.  Since calculating the
pixel-height of a large buffer can take some time, it makes sense to
specify this argument; in particular, if the caller does not know the
size of the buffer.

The optional argument @var{mode-and-header-line} @code{nil} or omitted
means to not include the height of the mode- or header-line of
@var{window} in the return value.  If it is either the symbol
@code{mode-line} or @code{header-line}, include only the height of that
line, if present, in the return value.  If it is @code{t}, include the
height of both, if present, in the return value.
@end defun


@node Line Height
@section Line Height
@cindex line height
@cindex height of a line

  The total height of each display line consists of the height of the
contents of the line, plus optional additional vertical line spacing
above or below the display line.

  The height of the line contents is the maximum height of any
character or image on that display line, including the final newline
if there is one.  (A display line that is continued doesn't include a
final newline.)  That is the default line height, if you do nothing to
specify a greater height.  (In the most common case, this equals the
height of the default frame font.)

  There are several ways to explicitly specify a larger line height,
either by specifying an absolute height for the display line, or by
specifying vertical space.  However, no matter what you specify, the
actual line height can never be less than the default.

@kindex line-height @r{(text property)}
  A newline can have a @code{line-height} text or overlay property
that controls the total height of the display line ending in that
newline.

  If the property value is @code{t}, the newline character has no
effect on the displayed height of the line---the visible contents
alone determine the height.  This is useful for tiling small images
(or image slices) without adding blank areas between the images.

  If the property value is a list of the form @code{(@var{height}
@var{total})}, that adds extra space @emph{below} the display line.
First Emacs uses @var{height} as a height spec to control extra space
@emph{above} the line; then it adds enough space @emph{below} the line
to bring the total line height up to @var{total}.  In this case, the
other ways to specify the line spacing are ignored.

@cindex height spec
  Any other kind of property value is a height spec, which translates
into a number---the specified line height.  There are several ways to
write a height spec; here's how each of them translates into a number:

@table @code
@item @var{integer}
If the height spec is a positive integer, the height value is that integer.
@item @var{float}
If the height spec is a float, @var{float}, the numeric height value
is @var{float} times the frame's default line height.
@item (@var{face} . @var{ratio})
If the height spec is a cons of the format shown, the numeric height
is @var{ratio} times the height of face @var{face}.  @var{ratio} can
be any type of number, or @code{nil} which means a ratio of 1.
If @var{face} is @code{t}, it refers to the current face.
@item (nil . @var{ratio})
If the height spec is a cons of the format shown, the numeric height
is @var{ratio} times the height of the contents of the line.
@end table

  Thus, any valid height spec determines the height in pixels, one way
or another.  If the line contents' height is less than that, Emacs
adds extra vertical space above the line to achieve the specified
total height.

  If you don't specify the @code{line-height} property, the line's
height consists of the contents' height plus the line spacing.
There are several ways to specify the line spacing for different
parts of Emacs text.

  On graphical terminals, you can specify the line spacing for all
lines in a frame, using the @code{line-spacing} frame parameter
(@pxref{Layout Parameters}).  However, if the default value of
@code{line-spacing} is non-@code{nil}, it overrides the
frame's @code{line-spacing} parameter.  An integer specifies the
number of pixels put below lines.  A floating-point number specifies
the spacing relative to the frame's default line height.

@vindex line-spacing
  You can specify the line spacing for all lines in a buffer via the
buffer-local @code{line-spacing} variable.  An integer specifies
the number of pixels put below lines.  A floating-point number
specifies the spacing relative to the default frame line height.  This
overrides line spacings specified for the frame.

@kindex line-spacing @r{(text property)}
  Finally, a newline can have a @code{line-spacing} text or overlay
property that overrides the default frame line spacing and the buffer
local @code{line-spacing} variable, for the display line ending in
that newline.

  One way or another, these mechanisms specify a Lisp value for the
spacing of each line.  The value is a height spec, and it translates
into a Lisp value as described above.  However, in this case the
numeric height value specifies the line spacing, rather than the line
height.

  On text terminals, the line spacing cannot be altered.

@node Faces
@section フェイス
@cindex フェイス

@dfn{フェイス}（face）とは、図形的な属性、つまり、
フォント、前景色、背景色、下線などの
の名前付きの集合体です。
フェイスはスクリーン上のテキスト
as well as
other parts of the frame such as the mode line.
の表示を制御します。

@cindex anonymous face
  One way to represent a face is as a property list of attributes,
like @code{(:foreground "red" :weight bold)}.  Such a list is called
an @dfn{anonymous face}.  For example, you can assign an anonymous
face as the value of the @code{face} text property, and Emacs will
display the underlying text with the specified attributes.
@xref{Special Properties}.

@cindex face name
  More commonly, a face is referred to via a @dfn{face name}: a Lisp
symbol associated with a set of face attributes@footnote{For backward
compatibility, you can also use a string to specify a face name; that
is equivalent to a Lisp symbol with the same name.}.  Named faces are
defined using the @code{defface} macro (@pxref{Defining Faces}).
Emacs comes with several standard named faces (@pxref{Basic Faces}).

  Many parts of Emacs required named faces, and do not accept
anonymous faces.  These include the functions documented in
@ref{Attribute Functions}, and the variable @code{font-lock-keywords}
(@pxref{Search-based Fontification}).  Unless otherwise stated, we
will use the term @dfn{face} to refer only to named faces.

@defun facep object
この関数は、@var{object}がフェイスの場合は、そのシンボル名か、
フェイス名を示す文字列である、@code{nil}でない値を返す。
さもなければ@code{nil}を返す。
@end defun

@menu
* Face Attributes::     What is in a face?
* Defining Faces::      How to define a face.
* Attribute Functions::  Functions to examine and set face attributes.
* Displaying Faces::     How Emacs combines the faces specified for a character.
* Face Remapping::      Remapping faces to alternative definitions.
* Face Functions::      How to define and examine faces.
* Auto Faces::          Hook for automatic face assignment.
* Basic Faces::         Faces that are defined by default.
* Font Selection::      Finding the best available font for a face.
* Font Lookup::         Looking up the names of available fonts
                          and information about them.
* Fontsets::            A fontset is a collection of fonts
                          that handle a range of character sets.
* Low-Level Font::      Lisp representation for character display fonts.
@end menu

@node Face Attributes
@subsection Face Attributes
@cindex face attributes

  @dfn{Face attributes} determine the visual appearance of a face.
The following table lists all the face attributes, their possible
values, and their effects.

  Apart from the values given below, each face attribute can have the
value @code{unspecified}.  This special value means that the face
doesn't specify that attribute directly.  An @code{unspecified}
attribute tells Emacs to refer instead to a parent face (see the
description @code{:inherit} attribute below); or, failing that, to an
underlying face (@pxref{Displaying Faces}).  The @code{default} face
must specify all attributes.

  Some of these attributes are meaningful only on certain kinds of
displays.  If your display cannot handle a certain attribute, the
attribute is ignored.

@table @code
@item :family
Font family or fontset (a string).  @xref{Fonts,,, emacs, The GNU
Emacs Manual}, for more information about font families.  The function
@code{font-family-list} (see below) returns a list of available family
names.  @xref{Fontsets}, for information about fontsets.

@item :foundry
The name of the @dfn{font foundry} for the font family specified by
the @code{:family} attribute (a string).  @xref{Fonts,,, emacs, The
GNU Emacs Manual}.

@item :width
Relative character width.  This should be one of the symbols
@code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
@code{semi-condensed}, @code{normal}, @code{semi-expanded},
@code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.

@item :height
The height of the font.  In the simplest case, this is an integer in
units of 1/10 point.

The value can also be floating point or a function, which
specifies the height relative to an @dfn{underlying face}
(@pxref{Displaying Faces}).  A floating-point value
specifies the amount by which to scale the height of the
underlying face.  A function value is called
with one argument, the height of the underlying face, and returns the
height of the new face.  If the function is passed an integer
argument, it must return an integer.

The height of the default face must be specified using an integer;
floating point and function values are not allowed.

@item :weight
Font weight---one of the symbols (from densest to faintest)
@code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
@code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
@code{ultra-light}.  On text terminals which support
variable-brightness text, any weight greater than normal is displayed
as extra bright, and any weight less than normal is displayed as
half-bright.

@cindex italic text
@item :slant
Font slant---one of the symbols @code{italic}, @code{oblique},
@code{normal}, @code{reverse-italic}, or @code{reverse-oblique}.  On
text terminals that support variable-brightness text, slanted text is
displayed as half-bright.

@item :foreground
Foreground color, a string.  The value can be a system-defined color
name, or a hexadecimal color specification.  @xref{Color Names}.  On
black-and-white displays, certain shades of gray are implemented by
stipple patterns.

@item :distant-foreground
Alternative foreground color, a string.  This is like @code{:foreground}
but the color is only used as a foreground when the background color is
near to the foreground that would have been used.  This is useful for
example when marking text (i.e., the region face).  If the text has a foreground
that is visible with the region face, that foreground is used.
If the foreground is near the region face background,
@code{:distant-foreground} is used instead so the text is readable.

@item :background
Background color, a string.  The value can be a system-defined color
name, or a hexadecimal color specification.  @xref{Color Names}.

@cindex underlined text
@item :underline
Whether or not characters should be underlined, and in what
way.  The possible values of the @code{:underline} attribute are:

@table @asis
@item @code{nil}
Don't underline.

@item @code{t}
Underline with the foreground color of the face.

@item @var{color}
Underline in color @var{color}, a string specifying a color.

@item @code{(:color @var{color} :style @var{style})}
@var{color} is either a string, or the symbol @code{foreground-color},
meaning the foreground color of the face.  Omitting the attribute
@code{:color} means to use the foreground color of the face.
@var{style} should be a symbol @code{line} or @code{wave}, meaning to
use a straight or wavy line.  Omitting the attribute @code{:style}
means to use a straight line.
@end table

@cindex overlined text
@item :overline
Whether or not characters should be overlined, and in what color.
If the value is @code{t}, overlining uses the foreground color of the
face.  If the value is a string, overlining uses that color.  The
value @code{nil} means do not overline.

@cindex strike-through text
@item :strike-through
Whether or not characters should be strike-through, and in what
color.  The value is used like that of @code{:overline}.

@cindex 2D box
@cindex 3D box
@item :box
Whether or not a box should be drawn around characters, its color, the
width of the box lines, and 3D appearance.  Here are the possible
values of the @code{:box} attribute, and what they mean:

@table @asis
@item @code{nil}
Don't draw a box.

@item @code{t}
Draw a box with lines of width 1, in the foreground color.

@item @var{color}
Draw a box with lines of width 1, in color @var{color}.

@item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
This way you can explicitly specify all aspects of the box.  The value
@var{width} specifies the width of the lines to draw; it defaults to
1.  A negative width @var{-n} means to draw a line of width @var{n}
that occupies the space of the underlying text, thus avoiding any
increase in the character height or width.

The value @var{color} specifies the color to draw with.  The default is
the foreground color of the face for simple boxes, and the background
color of the face for 3D boxes.

The value @var{style} specifies whether to draw a 3D box.  If it is
@code{released-button}, the box looks like a 3D button that is not being
pressed.  If it is @code{pressed-button}, the box looks like a 3D button
that is being pressed.  If it is @code{nil} or omitted, a plain 2D box
is used.
@end table

@item :inverse-video
Whether or not characters should be displayed in inverse video.  The
value should be @code{t} (yes) or @code{nil} (no).

@item :stipple
The background stipple, a bitmap.

The value can be a string; that should be the name of a file containing
external-format X bitmap data.  The file is found in the directories
listed in the variable @code{x-bitmap-file-path}.

Alternatively, the value can specify the bitmap directly, with a list
of the form @code{(@var{width} @var{height} @var{data})}.  Here,
@var{width} and @var{height} specify the size in pixels, and
@var{data} is a string containing the raw bits of the bitmap, row by
row.  Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
in the string (which should be a unibyte string for best results).
This means that each row always occupies at least one whole byte.

If the value is @code{nil}, that means use no stipple pattern.

Normally you do not need to set the stipple attribute, because it is
used automatically to handle certain shades of gray.

@item :font
The font used to display the face.  Its value should be a font object.
@xref{Low-Level Font}, for information about font objects, font specs,
and font entities.

When specifying this attribute using @code{set-face-attribute}
(@pxref{Attribute Functions}), you may also supply a font spec, a font
entity, or a string.  Emacs converts such values to an appropriate
font object, and stores that font object as the actual attribute
value.  If you specify a string, the contents of the string should be
a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
font name is an XLFD containing wildcards, Emacs chooses the first
font matching those wildcards.  Specifying this attribute also changes
the values of the @code{:family}, @code{:foundry}, @code{:width},
@code{:height}, @code{:weight}, and @code{:slant} attributes.

@cindex inheritance, for faces
@item :inherit
The name of a face from which to inherit attributes, or a list of face
names.  Attributes from inherited faces are merged into the face like
an underlying face would be, with higher priority than underlying
faces (@pxref{Displaying Faces}).  If a list of faces is used,
attributes from faces earlier in the list override those from later
faces.
@end table

@defun font-family-list &optional frame
This function returns a list of available font family names.  The
optional argument @var{frame} specifies the frame on which the text is
to be displayed; if it is @code{nil}, the selected frame is used.
@end defun

@defopt underline-minimum-offset
This variable specifies the minimum distance between the baseline and
the underline, in pixels, when displaying underlined text.
@end defopt

@defopt x-bitmap-file-path
This variable specifies a list of directories for searching
for bitmap files, for the @code{:stipple} attribute.
@end defopt

@defun bitmap-spec-p object
This returns @code{t} if @var{object} is a valid bitmap specification,
suitable for use with @code{:stipple} (see above).  It returns
@code{nil} otherwise.
@end defun

@node Defining Faces
@subsection フェイスを定義する
@cindex defining faces

@cindex face spec
新たなフェイスを定義する方法は、@code{defface}を使うことです。
This macro associates a face name (a symbol) with a default @dfn{face
spec}.  A face spec is a construct which specifies what attributes a
face should have on any given terminal; for example, a face spec might
specify one foreground color on high-color terminals, and a different
foreground color on low-color terminals.

  People are sometimes tempted to create a variable whose value is a
face name.  In the vast majority of cases, this is not necessary; the
usual procedure is to define a face with @code{defface}, and then use
its name directly.

@defmac defface face spec doc [keyword value]@dots{}
このマクロは@var{spec}に従ったデフォルトを持つカスタマイズ可能なフェイスとして
@var{face}を宣言する。
シンボル@var{face}をクォートしないこと。
また、名前を@samp{-face}で終えてはならない。（冗長になる）
引数@var{doc}は、フェイスの説明文字列を指定する。
The additional @var{keyword} arguments have the same meanings as in
@code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).

If @var{face} already has a default face spec, this macro does
nothing.

The default face spec determines @var{face}'s appearance when no
customizations are in effect (@pxref{Customization}).  If @var{face}
has already been customized (via Custom themes or via customizations
read from the init file), its appearance is determined by the custom
face spec(s), which override the default face spec @var{spec}.
However, if the customizations are subsequently removed, the
appearance of @var{face} will again be determined by its default face
spec.

As an exception, if you evaluate a @code{defface} form with
@kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
of @code{eval-defun} overrides any custom face specs on the face,
causing the face to reflect exactly what the @code{defface} says.

The @var{spec} argument is a @dfn{face spec}, which states how the
face should appear on different kinds of terminals.  It should be an
alist whose elements each have the form

@example
(@var{display} . @var{plist})
@end example

@noindent
@var{display}は端末のクラスを指定する（下記参照）。
@var{plist}は、フェイス属性とその値の連想リストであり、各端末においてフェイスが
どのように現れるかを指定する。過去との互換性のため、要素を
@code{(@var{display} @var{plist})}と書くこともできる。

@var{spec}の要素の@var{display}部分は、要素を適用するフレームを決定する。
@var{spec}の1つより多くの要素が指定されたフレームに一致する場合、
そのフレームに一致した最初の要素だけを用いる。
@var{display}には３つの可能性がある。

@table @asis
@item @code{default}
This element of @var{spec} doesn't match any terminal; instead, it
specifies defaults that apply to all terminals.  This element, if
used, must be the first element of @var{spec}.  Each of the following
elements can override any or all of these defaults.

@item @code{t}
@var{spec}の要素はすべてのターミナルで一致する。
したがって、@var{spec}の以降の要素をけっして使わない。
通常、@code{t}は@var{spec}の最後の（あるいは唯一）の要素に使う。

@item リスト
@var{display}がリストであると、
各要素は@code{(@var{characteristic} @var{value}@dots{})}の形であること。
ここで、@var{characteristic}はターミナルの分類方法であり、
@var{value}は@var{display}を適用すべき分類とみなす値である。
特性@var{characteristic}の可能な値はつぎのとおりである。

@table @code
@item type
ターミナルが使用するウィンドウシステムの種類であり、
@code{graphic} （任意のグラフィック能力のあるディスプレイ）、
@code{x}、@code{pc}（MS-DOSのコンソール）、
@code{w32}（MS Windows 9X/NT）、@code{tty}（a non-graphics-capable display）
のいずれかである。
@xref{Window Systems, window-system}。

@item class
フレームで扱える表示色の種類であり、
@code{color}、@code{grayscale}、@code{mono}のいずれかである。

@item background
背景の種類であり、@code{light}か@code{dark}のいずれかである。

@item min-colors
An integer that represents the minimum number of colors the terminal
should support.  This matches a terminal if its
@code{display-color-cells} value is at least the specified integer.

@item supports
Whether or not the terminal can display the face attributes given in
@var{value}@dots{} (@pxref{Face Attributes}).  @xref{Display Face
Attribute Testing}, for more information on exactly how this testing
is done.
@end table

@var{display}の1つの要素において、
指定された@var{characteristic}に
1つより多くの@var{value}を指定すると、
それらのいずれの値でも受け入れる。
@var{display}に1つより多くの要素がある場合、
各要素は異なる@var{characteristic}を指定すること。
そうすれば、フレームの@emph{各}特性は
@var{display}に指定されたそのフレーム向けの
@var{value}の1つに一致するはずである。
@end table
@end defmac

  For example, here's the definition of the standard face
@code{highlight}:

@example
(defface highlight
  '((((class color) (min-colors 88) (background light))
     :background "darkseagreen2")
    (((class color) (min-colors 88) (background dark))
     :background "darkolivegreen")
    (((class color) (min-colors 16) (background light))
     :background "darkseagreen2")
    (((class color) (min-colors 16) (background dark))
     :background "darkolivegreen")
    (((class color) (min-colors 8))
     :background "green" :foreground "black")
    (t :inverse-video t))
  "Basic face for highlighting."
  :group 'basic-faces)
@end example

内部的には、Emacsは各フェイスのデフォルト指定を、その
@code{face-defface-spec}シンボル属性に格納する
（@pxref{Symbol Properties}）。
カスタマイズバッファでユーザーが保存した属性の記録には
@code{saved-face}が用いられる。
@code{customized-face}プロパティは、現在のセッションのみに適用される
カスタマイズされたフェイス指定を記録するが、保存はされない。また、
@code{theme-face}プロパティはアクティブなカスタ未設定と当該フェイスの
フェイス指定を持つカスタムテーマ保存する。
説明文字列は@code{face-documentation}に記録される。

  Normally, a face is declared just once, using @code{defface}, and
any further changes to its appearance are applied using the Customize
framework (e.g., via the Customize user interface or via the
@code{custom-set-faces} function; @pxref{Applying Customizations}), or
by face remapping (@pxref{Face Remapping}).  In the rare event that
you need to change a face spec directly from Lisp, you can use the
@code{face-spec-set} function.

@defun face-spec-set face spec &optional spec-type
This function applies @var{spec} as a face spec for @code{face}.
@var{spec} should be a face spec, as described in the above
documentation for @code{defface}.

This function also defines @var{face} as a valid face name if it is
not already one, and (re)calculates its attributes on existing frames.

@cindex override spec @r{(for a face)}
The argument @var{spec-type} determines which spec to set.  If it is
@code{nil} or @code{face-override-spec}, this function sets the
@dfn{override spec}, which overrides over all other face specs on
@var{face}.  If it is @code{customized-face} or @code{saved-face},
this function sets the customized spec or the saved custom spec.  If
it is @code{face-defface-spec}, this function sets the default face
spec (the same one set by @code{defface}).  If it is @code{reset},
this function clears out all customization specs and override specs
from @var{face} (in this case, the value of @var{spec} is ignored).
Any other value of @var{spec-type} is reserved for internal use.
@end defun

@node Attribute Functions
@subsection Face Attribute Functions
@cindex face attributes, access and modification

  This section describes functions for directly accessing and
modifying the attributes of a named face.

@defun face-attribute face attribute &optional frame inherit
This function returns the value of the @var{attribute} attribute for
@var{face} on @var{frame}.

If @var{frame} is @code{nil}, that means the selected frame
(@pxref{Input Focus}).  If @var{frame} is @code{t}, this function
returns the value of the specified attribute for newly-created frames
(this is normally @code{unspecified}, unless you have specified some
value using @code{set-face-attribute}; see below).

If @var{inherit} is @code{nil}, only attributes directly defined by
@var{face} are considered, so the return value may be
@code{unspecified}, or a relative value.  If @var{inherit} is
non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
with the faces specified by its @code{:inherit} attribute; however the
return value may still be @code{unspecified} or relative.  If
@var{inherit} is a face or a list of faces, then the result is further
merged with that face (or faces), until it becomes specified and
absolute.

To ensure that the return value is always specified and absolute, use
a value of @code{default} for @var{inherit}; this will resolve any
unspecified or relative values by merging with the @code{default} face
(which is always completely specified).

For example,

@example
(face-attribute 'bold :weight)
     @result{} bold
@end example
@end defun

@c FIXME: Add an index for "relative face attribute", maybe here?  --xfq
@defun face-attribute-relative-p attribute value
This function returns non-@code{nil} if @var{value}, when used as the
value of the face attribute @var{attribute}, is relative.  This means
it would modify, rather than completely override, any value that comes
from a subsequent face in the face list or that is inherited from
another face.

@code{unspecified} is a relative value for all attributes.  For
@code{:height}, floating point and function values are also relative.

For example:

@example
(face-attribute-relative-p :height 2.0)
     @result{} t
@end example
@end defun

@defun face-all-attributes face &optional frame
This function returns an alist of attributes of @var{face}.  The
elements of the result are name-value pairs of the form
@w{@code{(@var{attr-name} . @var{attr-value})}}.  Optional argument
@var{frame} specifies the frame whose definition of @var{face} to
return; if omitted or @code{nil}, the returned value describes the
default attributes of @var{face} for newly created frames.
@end defun

@defun merge-face-attribute attribute value1 value2
If @var{value1} is a relative value for the face attribute
@var{attribute}, returns it merged with the underlying value
@var{value2}; otherwise, if @var{value1} is an absolute value for the
face attribute @var{attribute}, returns @var{value1} unchanged.
@end defun

  Normally, Emacs uses the face specs of each face to automatically
calculate its attributes on each frame (@pxref{Defining Faces}).  The
function @code{set-face-attribute} can override this calculation by
directly assigning attributes to a face, either on a specific frame or
for all frames.  This function is mostly intended for internal usage.

@defun set-face-attribute face frame &rest arguments
This function sets one or more attributes of @var{face} for
@var{frame}.  The attributes specifies in this way override the face
spec(s) belonging to @var{face}.

The extra arguments @var{arguments} specify the attributes to set, and
the values for them.  They should consist of alternating attribute
names (such as @code{:family} or @code{:underline}) and values.  Thus,

@example
(set-face-attribute 'foo nil :weight 'bold :slant 'italic)
@end example

@noindent
sets the attribute @code{:weight} to @code{bold} and the attribute
@code{:slant} to @code{italic}.


If @var{frame} is @code{t}, this function sets the default attributes
for newly created frames.  If @var{frame} is @code{nil}, this function
sets the attributes for all existing frames, as well as for newly
created frames.
@end defun

  The following commands and functions mostly provide compatibility
with old versions of Emacs.  They work by calling
@code{set-face-attribute}.  Values of @code{t} and @code{nil} for
their @var{frame} argument are handled just like
@code{set-face-attribute} and @code{face-attribute}.  The commands
read their arguments using the minibuffer, if called interactively.

@deffn Command set-face-foreground face color &optional frame
@deffnx Command set-face-background face color &optional frame
これらの関数は、フェイス@var{face}の@code{:foreground}属性
（あるいは@code{:background}属性）として@var{color}を設定する。
@end deffn

@deffn Command set-face-stipple face pattern &optional frame
この関数は、フェイス@var{face}の@code{:stipple}属性を@var{pattern}に設定する。
@end deffn

@deffn Command set-face-font face font &optional frame
この関数は、フェイス@var{face}のフォント@code{:font}属性を@var{font}に設定する。
@end deffn

@defun set-face-bold face bold-p &optional frame
この関数は、フェイス@var{face}の@code{:weight}属性を、
@var{bold-p}が@code{nil}ならば@var{normal}に、
そうでなければ@var{bold}に設定する。
@end defun

@defun set-face-italic face italic-p &optional frame
この関数は、@var{italic-p}が@code{nil}ならば、
フェイス@var{face}の@code{:slant}属性を@var{normal}に設定する。
それ以外の場合は、@var{italic}に設定する。
@end defun

@defun set-face-underline face underline &optional frame
この関数は、フェイス@var{face}の@code{:underline}属性を
@var{underline}に設定する。
@end defun

@defun set-face-inverse-video face inverse-video-p &optional frame
This sets the @code{:inverse-video} attribute of @var{face} to
@var{inverse-video-p}.
@end defun

@deffn Command invert-face face &optional frame
フェイス@var{face}の前景色と背景色を入れ換える。
@end deffn

以下の関数は、フェイスの属性を調べます。これらは、古い版のEmacsとの互換性の
ために提供されます。
フレーム@var{frame}を指定しない場合、
新たなフレーム向けのデフォルトのデータを参照します。
@code{t}は新フレームのデフォルトデータを参照します。
フェイスが当該属性の値を定義していない場合は、@code{unspecified}を返します。
If @var{inherit} is @code{nil}, only an attribute directly defined by the
face is returned.  If @var{inherit} is non-@code{nil}, any faces
specified by its @code{:inherit} attribute are considered as well, and
if @var{inherit} is a face or a list of faces, then they are also
considered, until a specified attribute is found.  To ensure that the
return value is always specified, use a value of @code{default} for
@var{inherit}.

@defun face-font face &optional frame
この関数はフェイス@var{face}のフォントの名前を返す。
@end defun

@defun face-foreground face &optional frame inherit
@defunx face-background face &optional frame inherit
これらの関数は、フェイス@var{face}の前景色（あるいは背景色）を
文字列で返す。
@end defun

@defun face-stipple face &optional frame inherit
この関数は、フェイス@var{face}の背景点猫パターンの名前を返す。
なければ@code{nil}を返す。
@end defun

@defun face-bold-p face &optional frame inherit
この関数はフェイス@var{face}の@code{:weight}属性が、通常より太い場合
（すなわち、@code{semi-bold}, @code{bold}, @code{extra-bold}または
@code{ultra-bold}のいずれかの場合）、@code{nil}でない値を返す。
それ以外の場合は、@code{nil}を返す。
@end defun

@defun face-italic-p face &optional frame inherit
この関数はフェイス@var{face}の@code{:slant}属性が、
@code{italic}または@code{oblique}である場合、
@code{nil}でない値を返す。
それ以外の場合は、@code{nil}を返す。
@end defun

@defun face-underline-p face &optional frame inherit
この関数はフェイス@var{face}の@code{:underline}属性が、
@code{nil}でない場合、@code{nil}でない値を返す。
@end defun

@defun face-inverse-video-p face &optional frame inherit
This function returns non-@code{nil} if face @var{face} specifies
a non-@code{nil} @code{:inverse-video} attribute.
@end defun

@node Displaying Faces
@subsection Displaying Faces
@cindex displaying faces
@cindex face merging

Emacsがあるテキスト断片を表示する際、その視覚的な姿形は複数の異なる
フェイス指定によって決定される場合があります。
これらのさまざまなフェイスが一緒に指定された場合、Emacsは
Emacsは指定されたさまざまなフェイスの属性を併合します。
以下に、Emacsがフェイスを併合するか、その優先度を高い方から
順番に示します。

@itemize @bullet
@item
テキストが特別な字形から構成される場合、グリフは特定のフェイスを指定できる。
@xref{Glyphs}。

@item
If the text lies within an active region, Emacs highlights it using
the @code{region} face.  @xref{Standard Faces,,, emacs, The GNU Emacs
Manual}.

@item
If the text lies within an overlay with a non-@code{nil} @code{face}
property, Emacs applies the face(s) specified by that property.  If
the overlay has a @code{mouse-face} property and the mouse is ``near
enough'' to the overlay, Emacs applies the face or face attributes
specified by the @code{mouse-face} property instead.  @xref{Overlay
Properties}.

複数のオーバレイが1つの文字を覆う場合、
高い優先順位のオーバレイが低いものに優先します。
@xref{Overlays}。

@item
If the text contains a @code{face} or @code{mouse-face} property,
Emacs applies the specified faces and face attributes.  @xref{Special
Properties}.  (This is how Font Lock mode faces are applied.
@xref{Font Lock Mode}.)

@item
If the text lies within the mode line of the selected window, Emacs
applies the @code{mode-line} face.  For the mode line of a
non-selected window, Emacs applies the @code{mode-line-inactive} face.
For a header line, Emacs applies the @code{header-line} face.

@item
If any given attribute has not been specified during the preceding
steps, Emacs applies the attribute of the @code{default} face.
@end itemize

  At each stage, if a face has a valid @code{:inherit} attribute,
Emacs treats any attribute with an @code{unspecified} value as having
the corresponding value drawn from the parent face(s).  @pxref{Face
Attributes}.  Note that the parent face(s) may also leave the
attribute unspecified; in that case, the attribute remains unspecified
at the next level of face merging.

@node Face Remapping
@subsection Face Remapping
@cindex face remapping

  The variable @code{face-remapping-alist} is used for buffer-local or
global changes in the appearance of a face.  For instance, it is used
to implement the @code{text-scale-adjust} command (@pxref{Text
Scale,,, emacs, The GNU Emacs Manual}).

@defvar face-remapping-alist
The value of this variable is an alist whose elements have the form
@code{(@var{face} . @var{remapping})}.  This causes Emacs to display
any text having the face @var{face} with @var{remapping}, rather than
the ordinary definition of @var{face}.

@var{remapping} may be any face spec suitable for a @code{face} text
property: either a face (i.e., a face name or a property list of
attribute/value pairs), or a list of faces.  For details, see the
description of the @code{face} text property in @ref{Special
Properties}.  @var{remapping} serves as the complete specification for
the remapped face---it replaces the normal definition of @var{face},
instead of modifying it.

If @code{face-remapping-alist} is buffer-local, its local value takes
effect only within that buffer.

Note: face remapping is non-recursive.  If @var{remapping} references
the same face name @var{face}, either directly or via the
@code{:inherit} attribute of some other face in @var{remapping}, that
reference uses the normal definition of @var{face}.  For instance, if
the @code{mode-line} face is remapped using this entry in
@code{face-remapping-alist}:

@example
(mode-line italic mode-line)
@end example

@noindent
then the new definition of the @code{mode-line} face inherits from the
@code{italic} face, and the @emph{normal} (non-remapped) definition of
@code{mode-line} face.
@end defvar

@cindex relative remapping, faces
@cindex base remapping, faces
  The following functions implement a higher-level interface to
@code{face-remapping-alist}.  Most Lisp code should use these
functions instead of setting @code{face-remapping-alist} directly, to
avoid trampling on remappings applied elsewhere.  These functions are
intended for buffer-local remappings, so they all make
@code{face-remapping-alist} buffer-local as a side-effect. They manage
@code{face-remapping-alist} entries of the form

@example
  (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
@end example

@noindent
where, as explained above, each of the @var{relative-spec-N} and
@var{base-spec} is either a face name, or a property list of
attribute/value pairs.  Each of the @dfn{relative remapping} entries,
@var{relative-spec-N}, is managed by the
@code{face-remap-add-relative} and @code{face-remap-remove-relative}
functions; these are intended for simple modifications like changing
the text size.  The @dfn{base remapping} entry, @var{base-spec}, has
the lowest priority and is managed by the @code{face-remap-set-base}
and @code{face-remap-reset-base} functions; it is intended for major
modes to remap faces in the buffers they control.

@defun face-remap-add-relative face &rest specs
This function adds the face spec in @var{specs} as relative
remappings for face @var{face} in the current buffer.  The remaining
arguments, @var{specs}, should form either a list of face names, or a
property list of attribute/value pairs.

The return value is a Lisp object that serves as a ``cookie''; you can
pass this object as an argument to @code{face-remap-remove-relative}
if you need to remove the remapping later.

@example
;; Remap the `escape-glyph' face into a combination
;; of the `highlight' and `italic' faces:
(face-remap-add-relative 'escape-glyph 'highlight 'italic)

;; Increase the size of the `default' face by 50%:
(face-remap-add-relative 'default :height 1.5)
@end example
@end defun

@defun face-remap-remove-relative cookie
This function removes a relative remapping previously added by
@code{face-remap-add-relative}.  @var{cookie} should be the Lisp
object returned by @code{face-remap-add-relative} when the remapping
was added.
@end defun

@defun face-remap-set-base face &rest specs
This function sets the base remapping of @var{face} in the current
buffer to @var{specs}.  If @var{specs} is empty, the default base
remapping is restored, similar to calling @code{face-remap-reset-base}
(see below); note that this is different from @var{specs} containing a
single value @code{nil}, which has the opposite result (the global
definition of @var{face} is ignored).

This overwrites the default @var{base-spec}, which inherits the global
face definition, so it is up to the caller to add such inheritance if
so desired.
@end defun

@defun face-remap-reset-base face
This function sets the base remapping of @var{face} to its default
value, which inherits from @var{face}'s global definition.
@end defun

@node Face Functions
@subsection Functions for Working with Faces

以下は、フェイスを作成したり変更する補助関数です。

@defun face-list
この関数は、定義済みのすべてのフェイス名のリストを返す。
@end defun

@defun face-id face
この関数はフェイス@var{face}の@dfn{フェイス番号}（face number）を返します。
この番号はEmacs内部の下位レベルでフェイスを区別するために使われます。
しかし、フェイスをフェイス番号で参照することは極めてまれです。
@end defun

@defun face-documentation face
この関数はフェイス@var{face}の説明文字列を返す。
なければ@code{nil}を返す。
@end defun

@defun face-equal face1 face2 &optional frame
この関数は、フェイス@var{face1}と@var{face2}が
表示上の同じ属性を持てば@code{t}を返す。
@end defun

@defun face-differs-from-default-p face &optional frame
この関数は、フェイス@var{face}の表示がデフォルトのフェイスの表示と
異なる場合には@code{nil}でない値を返す。
@end defun

@cindex face alias
@cindex alias, for faces
A @dfn{face alias} provides an equivalent name for a face.  You can
define a face alias by giving the alias symbol the @code{face-alias}
property, with a value of the target face name.  The following example
makes @code{modeline} an alias for the @code{mode-line} face.

@example
(put 'modeline 'face-alias 'mode-line)
@end example

@defmac define-obsolete-face-alias obsolete-face current-face when
This macro defines @code{obsolete-face} as an alias for
@var{current-face}, and also marks it as obsolete, indicating that it
may be removed in future.  @var{when} should be a string indicating
when @code{obsolete-face} was made obsolete (usually a version number
string).
@end defmac

@node Auto Faces
@subsection Automatic Face Assignment
@cindex automatic face assignment
@cindex faces, automatic choice

  This hook is used for automatically assigning faces to text in the
buffer.  It is part of the implementation of Jit-Lock mode, used by
Font-Lock.

@defvar fontification-functions
This variable holds a list of functions that are called by Emacs
redisplay as needed, just before doing redisplay.  They are called even
when Font Lock Mode isn't enabled.  When Font Lock Mode is enabled, this
variable usually holds just one function, @code{jit-lock-function}.

The functions are called in the order listed, with one argument, a
buffer position @var{pos}.  Collectively they should attempt to assign
faces to the text in the current buffer starting at @var{pos}.

The functions should record the faces they assign by setting the
@code{face} property.  They should also add a non-@code{nil}
@code{fontified} property to all the text they have assigned faces to.
That property tells redisplay that faces have been assigned to that text
already.

It is probably a good idea for the functions to do nothing if the
character after @var{pos} already has a non-@code{nil} @code{fontified}
property, but this is not required.  If one function overrides the
assignments made by a previous one, the properties after the last
function finishes are the ones that really matter.

For efficiency, we recommend writing these functions so that they
usually assign faces to around 400 to 600 characters at each call.
@end defvar

@node Basic Faces
@subsection Basic Faces
@cindex basic faces

If your Emacs Lisp program needs to assign some faces to text, it is
often a good idea to use certain existing faces or inherit from them,
rather than defining entirely new faces.  This way, if other users
have customized the basic faces to give Emacs a certain look, your
program will ``fit in'' without additional customization.

  Some of the basic faces defined in Emacs are listed below.  In
addition to these, you might want to make use of the Font Lock faces
for syntactic highlighting, if highlighting is not already handled by
Font Lock mode, or if some Font Lock faces are not in use.
@xref{Faces for Font Lock}.

@table @code
@item default
属性が全て指定されたデフォルトのフェイスを使う。
All other faces
implicitly inherit from it: any unspecified attribute defaults to the
attribute on this face (@pxref{Face Attributes}).

@item bold
@itemx italic
@itemx bold-italic
@itemx underline
@itemx fixed-pitch
@itemx variable-pitch
These have the attributes indicated by their names (e.g., @code{bold}
has a bold @code{:weight} attribute), with all other attributes
unspecified (and so given by @code{default}).

@item shadow
For ``dimmed out'' text.  For example, it is used for the ignored
part of a filename in the minibuffer (@pxref{Minibuffer File,,
Minibuffers for File Names, emacs, The GNU Emacs Manual}).

@item link
@itemx link-visited
For clickable text buttons that send the user to a different
buffer or ``location''.

@item highlight
For stretches of text that should temporarily stand out.  For example,
it is commonly assigned to the @code{mouse-face} property for cursor
highlighting (@pxref{Special Properties}).

@item match
For text matching a search command.

@item error
@itemx warning
@itemx success
For text concerning errors, warnings, or successes.  For example,
these are used for messages in @file{*Compilation*} buffers.
@end table

@node Font Selection
@subsection Font Selection
@cindex font selection
@cindex selecting a font

  Before Emacs can draw a character on a graphical display, it must
select a @dfn{font} for that character@footnote{In this context, the
term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
Mode}).}.  @xref{Fonts,,, emacs, The GNU Emacs Manual}.  Normally,
Emacs automatically chooses a font based on the faces assigned to that
character---specifically, the face attributes @code{:family},
@code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
Attributes}).  The choice of font also depends on the character to be
displayed; some fonts can only display a limited set of characters.
If no available font exactly fits the requirements, Emacs looks for
the @dfn{closest matching font}.  The variables in this section
control how Emacs makes this selection.

@defopt face-font-family-alternatives
If a given family is specified but does not exist, this variable
specifies alternative font families to try.  Each element should have
this form:

@example
(@var{family} @var{alternate-families}@dots{})
@end example

If @var{family} is specified but not available, Emacs will try the other
families given in @var{alternate-families}, one by one, until it finds a
family that does exist.
@end defopt

@defopt face-font-selection-order
If there is no font that exactly matches all desired face attributes
(@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
this variable specifies the order in which these attributes should be
considered when selecting the closest matching font.  The value should
be a list containing those four attribute symbols, in order of
decreasing importance.  The default is @code{(:width :height :weight
:slant)}.

Font selection first finds the best available matches for the first
attribute in the list; then, among the fonts which are best in that
way, it searches for the best matches in the second attribute, and so
on.

The attributes @code{:weight} and @code{:width} have symbolic values in
a range centered around @code{normal}.  Matches that are more extreme
(farther from @code{normal}) are somewhat preferred to matches that are
less extreme (closer to @code{normal}); this is designed to ensure that
non-normal faces contrast with normal ones, whenever possible.

One example of a case where this variable makes a difference is when the
default font has no italic equivalent.  With the default ordering, the
@code{italic} face will use a non-italic font that is similar to the
default one.  But if you put @code{:slant} before @code{:height}, the
@code{italic} face will use an italic font, even if its height is not
quite right.
@end defopt

@defopt face-font-registry-alternatives
This variable lets you specify alternative font registries to try, if a
given registry is specified and doesn't exist.  Each element should have
this form:

@example
(@var{registry} @var{alternate-registries}@dots{})
@end example

If @var{registry} is specified but not available, Emacs will try the
other registries given in @var{alternate-registries}, one by one,
until it finds a registry that does exist.
@end defopt

@cindex scalable fonts
  Emacs can make use of scalable fonts, but by default it does not use
them.

@defopt scalable-fonts-allowed
This variable controls which scalable fonts to use.  A value of
@code{nil}, the default, means do not use scalable fonts.  @code{t}
means to use any scalable font that seems appropriate for the text.

Otherwise, the value must be a list of regular expressions.  Then a
scalable font is enabled for use if its name matches any regular
expression in the list.  For example,

@example
(setq scalable-fonts-allowed '("iso10646-1$"))
@end example

@noindent
allows the use of scalable fonts with registry @code{iso10646-1}.
@end defopt

@defvar face-font-rescale-alist
This variable specifies scaling for certain faces.  Its value should
be a list of elements of the form

@example
(@var{fontname-regexp} . @var{scale-factor})
@end example

If @var{fontname-regexp} matches the font name that is about to be
used, this says to choose a larger similar font according to the
factor @var{scale-factor}.  You would use this feature to normalize
the font size if certain fonts are bigger or smaller than their
nominal heights and widths would suggest.
@end defvar

@node Font Lookup
@subsection Looking Up Fonts
@cindex font lookup
@cindex looking up fonts

@defun x-list-fonts name &optional reference-face frame maximum width
この関数は、@var{name}に一致する
利用可能なフォント名のリストを返す。
@var{name} should be a string containing a font name in
either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
GNU Emacs Manual}).  
XLFD文字列中では、ワイルドカード文字を含んでいてもよい。
@samp{*}は任意の部分文字列に一致し、@samp{?}は任意の1文字に一致する。
フォント名とパターンの一致を取る際には、大文字小文字を区別しない。

省略可能な引数@var{reference-face}と@var{frame}を指定すると、
@var{frame}上にある@var{reference-face}（フェイス名）と同じサイズのフォントに
リストを制限する。

省略可能な引数@var{maximum}は、返すフォントの個数を制限する。
これが@code{nil}以外であると、戻り値は最初の@var{maximum}個の
一致したフォントに切り詰める。
@var{maximum}に小さな値を指定すると、
多くのフォントに一致する場合ではこの関数の動作がだいぶ速くなる。

The optional argument @var{width} specifies a desired font width.  If
it is non-@code{nil}, the function only returns those fonts whose
characters are (on average) @var{width} times as wide as
@var{reference-face}.
@end defun

@defun x-family-fonts &optional family frame
This function returns a list describing the available fonts for family
@var{family} on @var{frame}.  If @var{family} is omitted or @code{nil},
this list applies to all families, and therefore, it contains all
available fonts.  Otherwise, @var{family} must be a string; it may
contain the wildcards @samp{?} and @samp{*}.

The list describes the display that @var{frame} is on; if @var{frame} is
omitted or @code{nil}, it applies to the selected frame's display
(@pxref{Input Focus}).

Each element in the list is a vector of the following form:

@example
[@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
 @var{fixed-p} @var{full} @var{registry-and-encoding}]
@end example

The first five elements correspond to face attributes; if you
specify these attributes for a face, it will use this font.

The last three elements give additional information about the font.
@var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
@var{full} is the full name of the font, and
@var{registry-and-encoding} is a string giving the registry and
encoding of the font.
@end defun

@node Fontsets
@subsection Fontsets
@cindex fontset

@dfn{フォントセット}（fontset）は、フォントのリストであって、
各フォントが文字コードのある範囲に割り付けられています。
個々のフォントだけでは、Emacsが扱う文字集合の範囲全体を表示できませんが、
フォントセットならば可能です。
フォントセットにはフォントと同様に名前があり、
フレームやフェイス向けに『フォント』を指定するときの
フォント名のかわりにフォントセット名を使えます。
ここでは、Lispプログラムの制御のもとにフォントセットを定義することに
関する情報を述べます。

@defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
この関数は、指定文字列@var{fontset-spec}に従って
新たなフォントセットを定義する。
文字列はつぎの形であること。

@smallexample
@var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
@end smallexample

@noindent
コンマの前後の白文字は無視される。

文字列の始めの部分@var{fontpattern}は、
（最後の2つのフィールドが@samp{fontset-@var{alias}}であることを除いて）、
Xの標準フォント名であること。

新たなフォントセットには2つの名前、つまり、長い名前と短い名前がある。
長い名前は@var{fontpattern}そのものである。
短い名前は@samp{fontset-@var{alias}}である。
どちらの名前でもフォントセットを参照できる。
同じ名前のフォントセットがすでに存在する場合、
@var{noerror}が@code{nil}であるとエラーを通知し、
この関数はなにもしない。

省略可能な引数@var{style-variant-p}が@code{nil}以外であると、
フォントセットのbold（太字）、italic（斜体）、bold-italic（太字斜体）の
各変種も作成することを指示する。
これらの変種のフォントセットには短い名前はなく、
@var{fontpattern}のboldやitalicを変更して作った長い名前だけである。

指定文字列ではフォントセットで使うフォントも指定する。
詳しくは下記参照。
@end defun

@samp{@var{charset}:@var{font}}という構成は、
特定の1つの文字集合向けに（このフォントセットで）使うフォントを指定します。
ここで、@var{charset}は文字集合の名前であり、
@var{font}はその文字集合に使うフォントです。
この構成は、指定文字列で何回でも使えます。

明示してない残りの文字集合向けには、
@var{fontpattern}に基づいてEmacsがフォントを選びます。
つまり、@samp{fontset-@var{alias}}を1つの文字集合を指名する値で置き換えます。
@acronym{ASCII}文字集合向けには、
@samp{fontset-@var{alias}}を@samp{ISO8859-1}で置き換えます。

これに加えて、いくつか連続したフィールドがワイルドカードであるなら、
Emacsはそれらを1つのワイルドカードにまとめます。
これは、自動的に拡大縮小したフォントの使用を避けるためです。
大きめのフォントを縮小したフォントは編集には使えません。
また、小さめのフォントを拡大したフォントも有用ではありません。
というのは、Emacsがそうするように、
もともと小さなフォントを使うほうがよいからです。

したがって、@var{fontpattern}がつぎのようであると、

@example
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
@end example

@noindent
the font specification for @acronym{ASCII} characters would be this:
ASCII文字に対するフォント指定はつぎのようになります。

@example
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
@end example

@noindent
また、Chinese GB2312文字に対するフォント指定はつぎのようになります。

@example
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
@end example

上のフォント指定に一致する中国語フォントがないかもしれません。
多くのXの配布には、@var{family}フィールドが
@samp{song ti}か@samp{fangsong ti}の中国語フォントだけが含まれています。
そういった場合、@samp{Fontset-@var{n}}をつぎのように指定します。

@smallexample
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
        chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
@end smallexample

@noindent
そうすると、Chinese GB2312の文字を除くフォント指定では
@var{family}フィールドが@samp{fixed}となり、
Chinese GB2312の文字に対するフォント指定では
@var{family}フィールドが@samp{*}となります。

@defun set-fontset-font name character font-spec &optional frame add
This function modifies the existing fontset @var{name} to use the font
matching with @var{font-spec} for the character @var{character}.

If @var{name} is @code{nil}, this function modifies the fontset of the
selected frame or that of @var{frame} if @var{frame} is not
@code{nil}.

If @var{name} is @code{t}, this function modifies the default
fontset, whose short name is @samp{fontset-default}.

@var{character} may be a cons; @code{(@var{from} . @var{to})}, where
@var{from} and @var{to} are character codepoints.  In that case, use
@var{font-spec} for all characters in the range @var{from} and @var{to}
(inclusive).

@var{character} may be a charset.  In that case, use
@var{font-spec} for all character in the charsets.

@var{character} may be a script name.  In that case, use
@var{font-spec} for all character in the charsets.

@var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
where @var{family} is a family name of a font (possibly including a
foundry name at the head), @var{registry} is a registry name of a font
(possibly including an encoding name at the tail).

@var{font-spec} may be a font name string.

The optional argument @var{add}, if non-@code{nil}, specifies how to
add @var{font-spec} to the font specifications previously set.  If it
is @code{prepend}, @var{font-spec} is prepended.  If it is
@code{append}, @var{font-spec} is appended.  By default,
@var{font-spec} overrides the previous settings.

For instance, this changes the default fontset to use a font of which
family name is @samp{Kochi Gothic} for all characters belonging to
the charset @code{japanese-jisx0208}.

@smallexample
(set-fontset-font t 'japanese-jisx0208
                  (font-spec :family "Kochi Gothic"))
@end smallexample
@end defun

@defun char-displayable-p char
This function returns @code{t} if Emacs ought to be able to display
@var{char}.  More precisely, if the selected frame's fontset has a
font to display the character set that @var{char} belongs to.

Fontsets can specify a font on a per-character basis; when the fontset
does that, this function's value may not be accurate.
@end defun

@node Low-Level Font
@subsection Low-Level Font Representation
@cindex font property

  Normally, it is not necessary to manipulate fonts directly.  In case
you need to do so, this section explains how.

  In Emacs Lisp, fonts are represented using three different Lisp
object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
entities}.

@defun fontp object &optional type
Return @code{t} if @var{object} is a font object, font spec, or font
entity.  Otherwise, return @code{nil}.

The optional argument @var{type}, if non-@code{nil}, determines the
exact type of Lisp object to check for.  In that case, @var{type}
should be one of @code{font-object}, @code{font-spec}, or
@code{font-entity}.
@end defun

@cindex font object
  A font object is a Lisp object that represents a font that Emacs has
@dfn{opened}.  Font objects cannot be modified in Lisp, but they can
be inspected.

@defun font-at position &optional window string
Return the font object that is being used to display the character at
position @var{position} in the window @var{window}.  If @var{window}
is @code{nil}, it defaults to the selected window.  If @var{string} is
@code{nil}, @var{position} specifies a position in the current buffer;
otherwise, @var{string} should be a string, and @var{position}
specifies a position in that string.
@end defun

@cindex font spec
  A font spec is a Lisp object that contains a set of specifications
that can be used to find a font.  More than one font may match the
specifications in a font spec.

@defun font-spec &rest arguments
Return a new font spec using the specifications in @var{arguments},
which should come in @code{property}-@code{value} pairs.  The possible
specifications are as follows:

@table @code
@item :name
The font name (a string), in either XLFD, Fontconfig, or GTK format.
@xref{Fonts,,, emacs, The GNU Emacs Manual}.

@item :family
@itemx :foundry
@itemx :weight
@itemx :slant
@itemx :width
These have the same meanings as the face attributes of the same name.
@xref{Face Attributes}.

@item :size
The font size---either a non-negative integer that specifies the pixel
size, or a floating-point number that specifies the point size.

@item :adstyle
Additional typographic style information for the font, such as
@samp{sans}.  The value should be a string or a symbol.

@cindex font registry
@item :registry
The charset registry and encoding of the font, such as
@samp{iso8859-1}.  The value should be a string or a symbol.

@item :script
The script that the font must support (a symbol).

@item :otf
@cindex OpenType font
The font must be an OpenType font that supports these OpenType
features, provided Emacs is compiled with a library, such as
@samp{libotf} on GNU/Linux, that supports complex text layout for
scripts which need that.  The value must be a list of the form

@smallexample
@code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
@end smallexample

where @var{script-tag} is the OpenType script tag symbol;
@var{langsys-tag} is the OpenType language system tag symbol, or
@code{nil} to use the default language system; @code{gsub} is a list
of OpenType GSUB feature tag symbols, or @code{nil} if none is
required; and @code{gpos} is a list of OpenType GPOS feature tag
symbols, or @code{nil} if none is required.  If @code{gsub} or
@code{gpos} is a list, a @code{nil} element in that list means that
the font must not match any of the remaining tag symbols.  The
@code{gpos} element may be omitted.
@end table
@end defun

@defun font-put font-spec property value
Set the font property @var{property} in the font-spec @var{font-spec}
to @var{value}.
@end defun

@cindex font entity
  A font entity is a reference to a font that need not be open.  Its
properties are intermediate between a font object and a font spec:
like a font object, and unlike a font spec, it refers to a single,
specific font.  Unlike a font object, creating a font entity does not
load the contents of that font into computer memory.  Emacs may open
multiple font objects of different sizes from a single font entity
referring to a scalable font.

@defun find-font font-spec &optional frame
This function returns a font entity that best matches the font spec
@var{font-spec} on frame @var{frame}.  If @var{frame} is @code{nil},
it defaults to the selected frame.
@end defun

@defun list-fonts font-spec &optional frame num prefer
This function returns a list of all font entities that match the font
spec @var{font-spec}.

The optional argument @var{frame}, if non-@code{nil}, specifies the
frame on which the fonts are to be displayed.  The optional argument
@var{num}, if non-@code{nil}, should be an integer that specifies the
maximum length of the returned list.  The optional argument
@var{prefer}, if non-@code{nil}, should be another font spec, which is
used to control the order of the returned list; the returned font
entities are sorted in order of decreasing ``closeness'' to that font
spec.
@end defun

  If you call @code{set-face-attribute} and pass a font spec, font
entity, or font name string as the value of the @code{:font}
attribute, Emacs opens the best ``matching'' font that is available
for display.  It then stores the corresponding font object as the
actual value of the @code{:font} attribute for that face.

  The following functions can be used to obtain information about a
font.  For these functions, the @var{font} argument can be a font
object, a font entity, or a font spec.

@defun font-get font property
This function returns the value of the font property @var{property}
for @var{font}.

If @var{font} is a font spec and the font spec does not specify
@var{property}, the return value is @code{nil}.  If @var{font} is a
font object or font entity, the value for the @var{:script} property
may be a list of scripts supported by the font.
@end defun

@defun font-face-attributes font &optional frame
This function returns a list of face attributes corresponding to
@var{font}.  The optional argument @var{frame} specifies the frame on
which the font is to be displayed.  If it is @code{nil}, the selected
frame is used.  The return value has the form

@smallexample
(:family @var{family} :height @var{height} :weight @var{weight}
   :slant @var{slant} :width @var{width})
@end smallexample

where the values of @var{family}, @var{height}, @var{weight},
@var{slant}, and @var{width} are face attribute values.  Some of these
key-attribute pairs may be omitted from the list if they are not
specified by @var{font}.
@end defun

@defun font-xlfd-name font &optional fold-wildcards
This function returns the XLFD (X Logical Font Descriptor), a string,
matching @var{font}.  @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
information about XLFDs.  If the name is too long for an XLFD (which
can contain at most 255 characters), the function returns @code{nil}.

If the optional argument @var{fold-wildcards} is non-@code{nil},
consecutive wildcards in the XLFD are folded into one.
@end defun

The following two functions return important information about a font.

@defun font-info name &optional frame
This function returns information about a font specified by its
@var{name}, a string, as it is used on @var{frame}.  If @var{frame} is
omitted or @code{nil}, it defaults to the selected frame.

The value returned by the function is a vector of the form
@code{[@var{opened-name} @var{full-name} @var{size} @var{height}
@var{baseline-offset} @var{relative-compose} @var{default-ascent}
@var{max-width} @var{ascent} @var{descent} @var{space-width}
@var{average-width} @var{filename} @var{capability}]}.  Here's the
description of each components of this vector:

@table @var
@item opened-name
The name used to open the font, a string.

@item full-name
The full name of the font, a string.

@item size
The pixel size of the font.

@item height
The height of the font in pixels.

@item baseline-offset
The offset in pixels from the @acronym{ASCII} baseline, positive
upward.

@item relative-compose
@itemx default-ascent
Numbers controlling how to compose characters.

@item ascent
@itemx descent
The ascent and descent of this font.  The sum of these two numbers
should be equal to the value of @var{height} above.

@item space-width
The width, in pixels, of the font's space character.

@item average-width
The average width of the font characters.  If this is zero, Emacs uses
the value of @var{space-width} instead, when it calculates text layout
on display.

@item filename
The file name of the font as a string.  This can be @code{nil} if the
font back-end does not provide a way to find out the font's file name.

@item capability
A list whose first element is a symbol representing the font type, one
of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
@code{pcf}, or @code{bdf}.  For OpenType fonts, the list includes 2
additional elements describing the @sc{gsub} and @sc{gpos} features
supported by the font.  Each of these elements is a list of the form
@code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
@dots{})}, where @var{script} is a symbol representing an OpenType
script tag, @var{langsys} is a symbol representing an OpenType langsys
tag (or @code{nil}, which stands for the default langsys), and each
@var{feature} is a symbol representing an OpenType feature tag.
@end table
@end defun

@defun query-font font-object
This function returns information about a @var{font-object}.  (This is
in contrast to @code{font-info}, which takes the font name, a string,
as its argument.)

The value returned by the function is a vector of the form
@code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
@var{ascent} @var{descent} @var{space-width} @var{average-width}
@var{capability}]}.  Here's the description of each components of this
vector:

@table @var
@item name
The font name, a string.

@item filename
The file name of the font as a string.  This can be @code{nil} if the
font back-end does not provide a way to find out the font's file name.

@item pixel-size
The pixel size of the font used to open the font.

@item max-width
The maximum advance width of the font.

@item ascent
@itemx descent
The ascent and descent of this font.  The sum of these two numbers
gives the font height.

@item space-width
The width, in pixels, of the font's space character.

@item average-width
The average width of the font characters.  If this is zero, Emacs uses
the value of @var{space-width} instead, when it calculates text layout
on display.

@item capability
A list whose first element is a symbol representing the font type, one
of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
@code{pcf}, or @code{bdf}.  For OpenType fonts, the list includes 2
additional elements describing the @sc{gsub} and @sc{gpos} features
supported by the font.  Each of these elements is a list of the form
@code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
@dots{})}, where @var{script} is a symbol representing an OpenType
script tag, @var{langsys} is a symbol representing an OpenType langsys
tag (or @code{nil}, which stands for the default langsys), and each
@var{feature} is a symbol representing an OpenType feature tag.
@end table
@end defun

@node Fringes
@section Fringes
@cindex fringes

  On graphical displays, Emacs draws @dfn{fringes} next to each
window: thin vertical strips down the sides which can display bitmaps
indicating truncation, continuation, horizontal scrolling, and so on.

@menu
* Fringe Size/Pos::     Specifying where to put the window fringes.
* Fringe Indicators::   Displaying indicator icons in the window fringes.
* Fringe Cursors::      Displaying cursors in the right fringe.
* Fringe Bitmaps::      Specifying bitmaps for fringe indicators.
* Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
* Overlay Arrow::       Display of an arrow to indicate position.
@end menu

@node Fringe Size/Pos
@subsection Fringe Size and Position

  The following buffer-local variables control the position and width
of fringes in windows showing that buffer.

@defvar fringes-outside-margins
The fringes normally appear between the display margins and the window
text.  If the value is non-@code{nil}, they appear outside the display
margins.  @xref{Display Margins}.
@end defvar

@defvar left-fringe-width
This variable, if non-@code{nil}, specifies the width of the left
fringe in pixels.  A value of @code{nil} means to use the left fringe
width from the window's frame.
@end defvar

@defvar right-fringe-width
This variable, if non-@code{nil}, specifies the width of the right
fringe in pixels.  A value of @code{nil} means to use the right fringe
width from the window's frame.
@end defvar

  Any buffer which does not specify values for these variables uses
the values specified by the @code{left-fringe} and @code{right-fringe}
frame parameters (@pxref{Layout Parameters}).

  The above variables actually take effect via the function
@code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
@code{set-window-fringes} as a subroutine.  If you change one of these
variables, the fringe display is not updated in existing windows
showing the buffer, unless you call @code{set-window-buffer} again in
each affected window.  You can also use @code{set-window-fringes} to
control the fringe display in individual windows.

@defun set-window-fringes window left &optional right outside-margins
This function sets the fringe widths of window @var{window}.
If @var{window} is @code{nil}, the selected window is used.

The argument @var{left} specifies the width in pixels of the left
fringe, and likewise @var{right} for the right fringe.  A value of
@code{nil} for either one stands for the default width.  If
@var{outside-margins} is non-@code{nil}, that specifies that fringes
should appear outside of the display margins.
@end defun

@defun window-fringes &optional window
This function returns information about the fringes of a window
@var{window}.  If @var{window} is omitted or @code{nil}, the selected
window is used.  The value has the form @code{(@var{left-width}
@var{right-width} @var{outside-margins})}.
@end defun


@node Fringe Indicators
@subsection Fringe Indicators
@cindex fringe indicators
@cindex indicators, fringe

  @dfn{Fringe indicators} are tiny icons displayed in the window
fringe to indicate truncated or continued lines, buffer boundaries,
etc.

@defopt indicate-empty-lines
@cindex fringes, and empty line indication
@cindex empty lines, indicating
When this is non-@code{nil}, Emacs displays a special glyph in the
fringe of each empty line at the end of the buffer, on graphical
displays.  @xref{Fringes}.  This variable is automatically
buffer-local in every buffer.
@end defopt

@defopt indicate-buffer-boundaries
@cindex buffer boundaries, indicating
This buffer-local variable controls how the buffer boundaries and
window scrolling are indicated in the window fringes.

Emacs can indicate the buffer boundaries---that is, the first and last
line in the buffer---with angle icons when they appear on the screen.
In addition, Emacs can display an up-arrow in the fringe to show
that there is text above the screen, and a down-arrow to show
there is text below the screen.

There are three kinds of basic values:

@table @asis
@item @code{nil}
Don't display any of these fringe icons.
@item @code{left}
Display the angle icons and arrows in the left fringe.
@item @code{right}
Display the angle icons and arrows in the right fringe.
@item any non-alist
Display the angle icons in the left fringe
and don't display the arrows.
@end table

Otherwise the value should be an alist that specifies which fringe
indicators to display and where.  Each element of the alist should
have the form @code{(@var{indicator} . @var{position})}.  Here,
@var{indicator} is one of @code{top}, @code{bottom}, @code{up},
@code{down}, and @code{t} (which covers all the icons not yet
specified), while @var{position} is one of @code{left}, @code{right}
and @code{nil}.

For example, @code{((top . left) (t . right))} places the top angle
bitmap in left fringe, and the bottom angle bitmap as well as both
arrow bitmaps in right fringe.  To show the angle bitmaps in the left
fringe, and no arrow bitmaps, use @code{((top .  left) (bottom . left))}.
@end defopt

@defvar fringe-indicator-alist
This buffer-local variable specifies the mapping from logical fringe
indicators to the actual bitmaps displayed in the window fringes.  The
value is an alist of elements @code{(@var{indicator}
. @var{bitmaps})}, where @var{indicator} specifies a logical indicator
type and @var{bitmaps} specifies the fringe bitmaps to use for that
indicator.

  Each @var{indicator} should be one of the following symbols:

@table @asis
@item @code{truncation}, @code{continuation}.
Used for truncation and continuation lines.

@item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
@code{up} and @code{down} indicate a buffer boundary lying above or
below the window edge; @code{top} and @code{bottom} indicate the
topmost and bottommost buffer text line; and @code{top-bottom}
indicates where there is just one line of text in the buffer.

@item @code{empty-line}
Used to indicate empty lines when @code{indicate-empty-lines} is
non-@code{nil}.

@item @code{overlay-arrow}
Used for overlay arrows (@pxref{Overlay Arrow}).
@c Is this used anywhere?
@c @item Unknown bitmap indicator:
@c @code{unknown}.
@end table

  Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
@var{right} [@var{left1} @var{right1}])}.  The @var{left} and
@var{right} symbols specify the bitmaps shown in the left and/or right
fringe, for the specific indicator.  @var{left1} and @var{right1} are
specific to the @code{bottom} and @code{top-bottom} indicators, and
are used to indicate that the last text line has no final newline.
Alternatively, @var{bitmaps} may be a single symbol which is used in
both left and right fringes.

  @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
to define your own.  In addition, @code{nil} represents the empty
bitmap (i.e., an indicator that is not shown).

  When @code{fringe-indicator-alist} has a buffer-local value, and
there is no bitmap defined for a logical indicator, or the bitmap is
@code{t}, the corresponding value from the default value of
@code{fringe-indicator-alist} is used.
@end defvar

@node Fringe Cursors
@subsection Fringe Cursors
@cindex fringe cursors
@cindex cursor, fringe

  When a line is exactly as wide as the window, Emacs displays the
cursor in the right fringe instead of using two lines.  Different
bitmaps are used to represent the cursor in the fringe depending on
the current buffer's cursor type.

@defopt overflow-newline-into-fringe
If this is non-@code{nil}, lines exactly as wide as the window (not
counting the final newline character) are not continued.  Instead,
when point is at the end of the line, the cursor appears in the right
fringe.
@end defopt

@defvar fringe-cursor-alist
This variable specifies the mapping from logical cursor type to the
actual fringe bitmaps displayed in the right fringe.  The value is an
alist where each element has the form @code{(@var{cursor-type}
. @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
display cursors of type @var{cursor-type}.

Each @var{cursor-type} should be one of @code{box}, @code{hollow},
@code{bar}, @code{hbar}, or @code{hollow-small}.  The first four have
the same meanings as in the @code{cursor-type} frame parameter
(@pxref{Cursor Parameters}).  The @code{hollow-small} type is used
instead of @code{hollow} when the normal @code{hollow-rectangle}
bitmap is too tall to fit on a specific display line.

Each @var{bitmap} should be a symbol specifying the fringe bitmap to
be displayed for that logical cursor type.
@iftex
See the next subsection for details.
@end iftex
@ifnottex
@xref{Fringe Bitmaps}.
@end ifnottex

@c FIXME: I can't find the fringes-indicator-alist variable.  Maybe
@c it should be fringe-indicator-alist or fringe-cursor-alist?  --xfq
When @code{fringe-cursor-alist} has a buffer-local value, and there is
no bitmap defined for a cursor type, the corresponding value from the
default value of @code{fringes-indicator-alist} is used.
@end defvar

@node Fringe Bitmaps
@subsection Fringe Bitmaps
@cindex fringe bitmaps
@cindex bitmaps, fringe

  The @dfn{fringe bitmaps} are the actual bitmaps which represent the
logical fringe indicators for truncated or continued lines, buffer
boundaries, overlay arrows, etc.  Each bitmap is represented by a
symbol.
@iftex
These symbols are referred to by the variables
@code{fringe-indicator-alist} and @code{fringe-cursor-alist},
described in the previous subsections.
@end iftex
@ifnottex
These symbols are referred to by the variable
@code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
(@pxref{Fringe Indicators}), and the variable
@code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
(@pxref{Fringe Cursors}).
@end ifnottex

  Lisp programs can also directly display a bitmap in the left or
right fringe, by using a @code{display} property for one of the
characters appearing in the line (@pxref{Other Display Specs}).  Such
a display specification has the form

@example
(@var{fringe} @var{bitmap} [@var{face}])
@end example

@noindent
@var{fringe} is either the symbol @code{left-fringe} or
@code{right-fringe}.  @var{bitmap} is a symbol identifying the bitmap
to display.  The optional @var{face} names a face whose foreground
color is used to display the bitmap; this face is automatically merged
with the @code{fringe} face.

  Here is a list of the standard fringe bitmaps defined in Emacs, and
how they are currently used in Emacs (via
@code{fringe-indicator-alist} and @code{fringe-cursor-alist}):

@table @asis
@item @code{left-arrow}, @code{right-arrow}
Used to indicate truncated lines.

@item @code{left-curly-arrow}, @code{right-curly-arrow}
Used to indicate continued lines.

@item @code{right-triangle}, @code{left-triangle}
The former is used by overlay arrows.  The latter is unused.

@item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
@itemx @code{bottom-left-angle}, @code{bottom-right-angle}
@itemx @code{top-right-angle}, @code{top-left-angle}
@itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
Used to indicate buffer boundaries.

@item @code{filled-rectangle}, @code{hollow-rectangle}
@itemx @code{filled-square}, @code{hollow-square}
@itemx @code{vertical-bar}, @code{horizontal-bar}
Used for different types of fringe cursors.

@item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
Not used by core Emacs features.
@end table

@noindent
The next subsection describes how to define your own fringe bitmaps.

@defun fringe-bitmaps-at-pos &optional pos window
This function returns the fringe bitmaps of the display line
containing position @var{pos} in window @var{window}.  The return
value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
is the symbol for the fringe bitmap in the left fringe (or @code{nil}
if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
is non-@code{nil} if there is an overlay arrow in the left fringe.

The value is @code{nil} if @var{pos} is not visible in @var{window}.
If @var{window} is @code{nil}, that stands for the selected window.
If @var{pos} is @code{nil}, that stands for the value of point in
@var{window}.
@end defun

@node Customizing Bitmaps
@subsection Customizing Fringe Bitmaps
@cindex fringe bitmaps, customizing

@defun define-fringe-bitmap bitmap bits &optional height width align
This function defines the symbol @var{bitmap} as a new fringe bitmap,
or replaces an existing bitmap with that name.

The argument @var{bits} specifies the image to use.  It should be
either a string or a vector of integers, where each element (an
integer) corresponds to one row of the bitmap.  Each bit of an integer
corresponds to one pixel of the bitmap, where the low bit corresponds
to the rightmost pixel of the bitmap.

The height is normally the length of @var{bits}.  However, you
can specify a different height with non-@code{nil} @var{height}.  The width
is normally 8, but you can specify a different width with non-@code{nil}
@var{width}.  The width must be an integer between 1 and 16.

The argument @var{align} specifies the positioning of the bitmap
relative to the range of rows where it is used; the default is to
center the bitmap.  The allowed values are @code{top}, @code{center},
or @code{bottom}.

The @var{align} argument may also be a list @code{(@var{align}
@var{periodic})} where @var{align} is interpreted as described above.
If @var{periodic} is non-@code{nil}, it specifies that the rows in
@code{bits} should be repeated enough times to reach the specified
height.
@end defun

@defun destroy-fringe-bitmap bitmap
This function destroy the fringe bitmap identified by @var{bitmap}.
If @var{bitmap} identifies a standard fringe bitmap, it actually
restores the standard definition of that bitmap, instead of
eliminating it entirely.
@end defun

@defun set-fringe-bitmap-face bitmap &optional face
This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
If @var{face} is @code{nil}, it selects the @code{fringe} face.  The
bitmap's face controls the color to draw it in.

@var{face} is merged with the @code{fringe} face, so normally
@var{face} should specify only the foreground color.
@end defun

@node Overlay Arrow
@subsection オーバレイ矢印
@c @cindex overlay arrow  Duplicates variable names

@dfn{オーバレイ矢印}（overlay arrow）は、
バッファの特定の行にユーザーの注意を向けるために有用です。
たとえば、デバッガとのインターフェイスを取るためのモードでは、
オーバレイ矢印で実行するコードの行を示します。
この機能は@dfn{オーバレイ}とは何の関係もありません。
（@pxref{Overlays}）。

@defvar overlay-arrow-string
この変数は、特定の行に注意を向けるために表示する文字列を保持する。
矢印機能を使っていなければ@code{nil}である。
On a graphical display the contents of the string are ignored; instead a
glyph is displayed in the fringe area to the left of the display area.
@end defvar

@defvar overlay-arrow-position
この変数は、オーバレイ矢印を表示する箇所を表すマーカを保持する。
行頭を指すこと。
非グラフィック表示では、矢印のテキストはその行の先頭に現れ、
その場所に本来現れるべきテキストを隠す。
矢印は普通は短く、行には字下げがあるので、
重要なものは普通はなにも上書きされない。

オーバレイ矢印文字列は、変数@code{overlay-arrow-position}の値が示す
マーカが指すバッファでのみ表示される。
そのため、@code{overlay-arrow-position}をバッファローカル
変数にすることで、複数のオーバレイ矢印を表示できる。
ただし、通常、複数のオーバレイ矢印表示には
@code{overlay-arrow-variable-list}を用いる。
@c !!! overlay-arrow-position: but the overlay string may remain in the display
@c of some other buffer until an update is required.  This should be fixed
@c now.  Is it?
@end defvar

同様のことは、属性@code{before-string}のオーバレイを
作成してもできます。
@xref{Overlay Properties}。

  You can define multiple overlay arrows via the variable
@code{overlay-arrow-variable-list}.

@defvar overlay-arrow-variable-list
This variable's value is a list of variables, each of which specifies
the position of an overlay arrow.  The variable
@code{overlay-arrow-position} has its normal meaning because it is on
this list.
@end defvar

Each variable on this list can have properties
@code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
specify an overlay arrow string (for text terminals) or fringe bitmap
(for graphical terminals) to display at the corresponding overlay
arrow position.  If either property is not set, the default
@code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
is used.


@node Scroll Bars
@section Scroll Bars
@cindex scroll bars

Normally the frame parameter @code{vertical-scroll-bars} controls
whether the windows in the frame have vertical scroll bars, and whether
they are on the left or right.  The frame parameter
@code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
the default).

   The frame parameter @code{horizontal-scroll-bars} controls whether
the windows in the frame have horizontal scroll bars.  The frame
parameter @code{scroll-bar-height} specifies how high they are
(@code{nil} meaning the default).  @xref{Layout Parameters}.

@vindex horizontal-scroll-bars-available-p
   Horizontal scroll bars are not available on all platforms.  The
function @code{horizontal-scroll-bars-available-p} which takes no
argument returns non-@code{nil} if they are available on your system.

   The following three functions take as argument a live frame which
defaults to the selected one.

@defun frame-current-scroll-bars &optional frame
This function reports the scroll bar types for frame @var{frame}.  The
value is a cons cell @code{(@var{vertical-type} .@:
@var{horizontal-type})}, where @var{vertical-type} is either
@code{left}, @code{right}, or @code{nil} (which means no vertical scroll
bar.)  @var{horizontal-type} is either @code{bottom} or @code{nil}
(which means no horizontal scroll bar).
@end defun

@defun frame-scroll-bar-width &optional Lisp_Object &optional frame
This function returns the width of vertical scroll bars of @var{frame}
in pixels.
@end defun

@defun frame-scroll-bar-height &optional Lisp_Object &optional frame
This function returns the height of horizontal scroll bars of
@var{frame} in pixels.
@end defun

You can override the frame specific settings for individual windows by
using the following function:

@defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
This function sets the width and/or height and the types of scroll bars
for window @var{window}.

@var{width} specifies the width of the vertical scroll bar in pixels
(@code{nil} means use the width specified for the frame).
@var{vertical-type} specifies whether to have a vertical scroll bar and,
if so, where.  The possible values are @code{left}, @code{right},
@code{t}, which means to use the frame's default, and @code{nil} for no
vertical scroll bar.

@var{height} specifies the height of the horizontal scroll bar in pixels
(@code{nil} means use the height specified for the frame).
@var{horizontal-type} specifies whether to have a horizontal scroll bar.
The possible values are @code{bottom}, @code{t}, which means to use the
frame's default, and @code{nil} for no horizontal scroll bar.

If @var{window} is @code{nil}, the selected window is used.
@end defun

The following four functions take as argument a live window which
defaults to the selected one.

@defun window-scroll-bars &optional window
This function returns a list of the form @code{(@var{width}
@var{columns} @var{vertical-type} @var{height} @var{lines}
@var{horizontal-type})}.

The value @var{width} is the value that was specified for the width of
the vertical scroll bar (which may be @code{nil}); @var{columns} is the
(possibly rounded) number of columns that the vertical scroll bar
actually occupies.

The value @var{height} is the value that was specified for the height of
the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
(possibly rounded) number of lines that the horizontally scroll bar
actually occupies.
@end defun

@defun window-current-scroll-bars &optional window
This function reports the scroll bar type for window @var{window}.  The
value is a cons cell @code{(@var{vertical-type} .@:
@var{horizontal-type})}.  Unlike @code{window-scroll-bars}, this reports
the scroll bar type actually used, once frame defaults and
@code{scroll-bar-mode} are taken into account.
@end defun

@defun window-scroll-bar-width &optional window
This function returns the width in pixels of @var{window}'s vertical
scrollbar.
@end defun

@defun window-scroll-bar-height &optional window
This function returns the height in pixels of @var{window}'s horizontal
scrollbar.
@end defun

If you don't specify these values for a window with
@code{set-window-scroll-bars}, the buffer-local variables
@code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
@code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
displayed control the window's scroll bars.  The function
@code{set-window-buffer} examines these variables.  If you change them
in a buffer that is already visible in a window, you can make the window
take note of the new values by calling @code{set-window-buffer}
specifying the same buffer that is already displayed.

You can control the appearance of scroll bars for a particular buffer by
setting the following variables which automatically become buffer-local
when set.

@defvar vertical-scroll-bar
This variable specifies the location of the vertical scroll bar.  The
possible values are @code{left}, @code{right}, @code{t}, which means to
use the frame's default, and @code{nil} for no scroll bar.
@end defvar

@defvar horizontal-scroll-bar
This variable specifies the location of the horizontal scroll bar.  The
possible values are @code{bottom}, @code{t}, which means to use the
frame's default, and @code{nil} for no scroll bar.
@end defvar

@defvar scroll-bar-width
This variable specifies the width of the buffer's vertical scroll bars,
measured in pixels.  A value of @code{nil} means to use the value
specified by the frame.
@end defvar

@defvar scroll-bar-height
This variable specifies the height of the buffer's horizontal scroll
bar, measured in pixels.  A value of @code{nil} means to use the value
specified by the frame.
@end defvar

Finally you can toggle the display of scroll bars on all frames by
customizing the variables @code{scroll-bar-mode} and
@code{horizontal-scroll-bar-mode}.

@defopt scroll-bar-mode
This variable controls whether and where to put vertical scroll bars in
all frames.  The possible values are @code{nil} for no scroll bars,
@code{left} to put scroll bars on the left and @code{right} to put
scroll bars on the right.
@end defopt

@defopt horizontal-scroll-bar-mode
This variable controls whether to display horizontal scroll bars on all
frames.
@end defopt


@node Window Dividers
@section Window Dividers
@cindex window dividers
@cindex right dividers
@cindex bottom dividers

Window dividers are bars drawn between a frame's windows.  A ``right''
divider is drawn between a window and any adjacent windows on the right.
Its width (thickness) is specified by the frame parameter
@code{right-divider-width}.  A ``bottom'' divider is drawn between a
window and adjacent windows on the bottom or the echo area.  Its width
is specified by the frame parameter @code{bottom-divider-width}.  In
either case, specifying a width of zero means to not draw such dividers.
@xref{Layout Parameters}.

   Technically, a right divider ``belongs'' to the window on its left,
which means that its width contributes to the total width of that
window.  A bottom divider ``belongs'' to the window above it, which
means that its width contributes to the total height of that window.
@xref{Window Sizes}.  When a window has both, a right and a bottom
divider, the bottom divider ``prevails''.  This means that a bottom
divider is drawn over the full total width of its window while the right
divider ends above the bottom divider.

   Dividers can be dragged with the mouse and are therefore useful for
adjusting the sizes of adjacent windows with the mouse.  They also serve
to visually set apart adjacent windows when no scroll bars or mode lines
are present.  The following three faces allow to customize the
appearance of dividers:

@table @code
@item window-divider
When a divider is less than three pixels wide, it is drawn solidly with
the foreground of this face.  For larger dividers this face is used for
the inner part only, excluding the first and last pixel.

@item window-divider-first-pixel
This is the face used for drawing the first pixel of a divider that is
at least three pixels wide.  To obtain a solid appearance, set this to
the same value used for the @code{window-divider} face.

@item window-divider-last-pixel
This is the face used for drawing the last pixel of a divider that is at
least three pixels wide.  To obtain a solid appearance, set this to the
same value used for the @code{window-divider} face.
@end table

You can get the sizes of the dividers of a specific window with the
following two functions.

@defun window-right-divider-width &optional window
Return the width (thickness) in pixels of @var{window}'s right divider.
@var{window} must be a live window and defaults to the selected one.
The return value is always zero for a rightmost window.
@end defun

@defun window-bottom-divider-width &optional window
Return the width (thickness) in pixels of @var{window}'s bottom divider.
@var{window} must be a live window and defaults to the selected one.
The return value is zero for the minibuffer window or a bottommost
window on a minibuffer-less frame.
@end defun


@node Display Property
@section The @code{display} Property
@cindex display specification
@kindex display @r{(text property)}

  The @code{display} text property (or overlay property) is used to
insert images into text, and to control other aspects of how text
displays.  The value of the @code{display} property should be a
display specification, or a list or vector containing several display
specifications.  Display specifications in the same @code{display}
property value generally apply in parallel to the text they cover.

  If several sources (overlays and/or a text property) specify values
for the @code{display} property, only one of the values takes effect,
following the rules of @code{get-char-property}.  @xref{Examining
Properties}.

  The rest of this section describes several kinds of
display specifications and what they mean.

@menu
* Replacing Specs::      Display specs that replace the text.
* Specified Space::      Displaying one space with a specified width.
* Pixel Specification::  Specifying space width or height in pixels.
* Other Display Specs::     Displaying an image; adjusting the height,
                              spacing, and other properties of text.
* Display Margins::     Displaying text or images to the side of the main text.
@end menu

@node Replacing Specs
@subsection Display Specs That Replace The Text
@cindex replacing display specs

  Some kinds of display specifications specify something to display
instead of the text that has the property.  These are called
@dfn{replacing} display specifications.  Emacs does not allow the user
to interactively move point into the middle of buffer text that is
replaced in this way.

  If a list of display specifications includes more than one replacing
display specification, the first overrides the rest.  Replacing
display specifications make most other display specifications
irrelevant, since those don't apply to the replacement.

  For replacing display specifications, ``the text that has the
property'' means all the consecutive characters that have the same
Lisp object as their @code{display} property; these characters are
replaced as a single unit.  If two characters have different Lisp
objects as their @code{display} properties (i.e., objects which are
not @code{eq}), they are handled separately.

  Here is an example which illustrates this point.  A string serves as
a replacing display specification, which replaces the text that has
the property with the specified string (@pxref{Other Display Specs}).
Consider the following function:

@smallexample
(defun foo ()
  (dotimes (i 5)
    (let ((string (concat "A"))
          (start (+ i i (point-min))))
      (put-text-property start (1+ start) 'display string)
      (put-text-property start (+ 2 start) 'display string))))
@end smallexample

@noindent
This function gives each of the first ten characters in the buffer a
@code{display} property which is a string @code{"A"}, but they don't
all get the same string object.  The first two characters get the same
string object, so they are replaced with one @samp{A}; the fact that
the display property was assigned in two separate calls to
@code{put-text-property} is irrelevant.  Similarly, the next two
characters get a second string (@code{concat} creates a new string
object), so they are replaced with one @samp{A}; and so on.  Thus, the
ten characters appear as five A's.

@node Specified Space
@subsection Specified Spaces
@cindex spaces, specified height or width
@cindex variable-width spaces

  To display a space of specified width and/or height, use a display
specification of the form @code{(space . @var{props})}, where
@var{props} is a property list (a list of alternating properties and
values).  You can put this property on one or more consecutive
characters; a space of the specified height and width is displayed in
place of @emph{all} of those characters.  These are the properties you
can use in @var{props} to specify the weight of the space:

@table @code
@item :width @var{width}
If @var{width} is a number, it specifies
that the space width should be @var{width} times the normal character
width.  @var{width} can also be a @dfn{pixel width} specification
(@pxref{Pixel Specification}).

@item :relative-width @var{factor}
Specifies that the width of the stretch should be computed from the
first character in the group of consecutive characters that have the
same @code{display} property.  The space width is the width of that
character, multiplied by @var{factor}.

@item :align-to @var{hpos}
Specifies that the space should be wide enough to reach @var{hpos}.
If @var{hpos} is a number, it is measured in units of the normal
character width.  @var{hpos} can also be a @dfn{pixel width}
specification (@pxref{Pixel Specification}).
@end table

  You should use one and only one of the above properties.  You can
also specify the height of the space, with these properties:

@table @code
@item :height @var{height}
Specifies the height of the space.
If @var{height} is a number, it specifies
that the space height should be @var{height} times the normal character
height.  The @var{height} may also be a @dfn{pixel height} specification
(@pxref{Pixel Specification}).

@item :relative-height @var{factor}
Specifies the height of the space, multiplying the ordinary height
of the text having this display specification by @var{factor}.

@item :ascent @var{ascent}
If the value of @var{ascent} is a non-negative number no greater than
100, it specifies that @var{ascent} percent of the height of the space
should be considered as the ascent of the space---that is, the part
above the baseline.  The ascent may also be specified in pixel units
with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).

@end table

  Don't use both @code{:height} and @code{:relative-height} together.

  The @code{:width} and @code{:align-to} properties are supported on
non-graphic terminals, but the other space properties in this section
are not.

  Note that space properties are treated as paragraph separators for
the purposes of reordering bidirectional text for display.
@xref{Bidirectional Display}, for the details.

@node Pixel Specification
@subsection Pixel Specification for Spaces
@cindex spaces, pixel specification

  The value of the @code{:width}, @code{:align-to}, @code{:height},
and @code{:ascent} properties can be a special kind of expression that
is evaluated during redisplay.  The result of the evaluation is used
as an absolute number of pixels.

  The following expressions are supported:

@smallexample
@group
  @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
  @var{num}  ::= @var{integer} | @var{float} | @var{symbol}
  @var{unit} ::= in | mm | cm | width | height
@end group
@group
  @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
        |  scroll-bar | text
  @var{pos}  ::= left | center | right
  @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
  @var{op}   ::= + | -
@end group
@end smallexample

  The form @var{num} specifies a fraction of the default frame font
height or width.  The form @code{(@var{num})} specifies an absolute
number of pixels.  If @var{num} is a symbol, @var{symbol}, its
buffer-local variable binding is used.

  The @code{in}, @code{mm}, and @code{cm} units specify the number of
pixels per inch, millimeter, and centimeter, respectively.  The
@code{width} and @code{height} units correspond to the default width
and height of the current face.  An image specification @code{image}
corresponds to the width or height of the image.

  The elements @code{left-fringe}, @code{right-fringe},
@code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
@code{text} specify to the width of the corresponding area of the
window.

  The @code{left}, @code{center}, and @code{right} positions can be
used with @code{:align-to} to specify a position relative to the left
edge, center, or right edge of the text area.

  Any of the above window elements (except @code{text}) can also be
used with @code{:align-to} to specify that the position is relative to
the left edge of the given area.  Once the base offset for a relative
position has been set (by the first occurrence of one of these
symbols), further occurrences of these symbols are interpreted as the
width of the specified area.  For example, to align to the center of
the left-margin, use

@example
:align-to (+ left-margin (0.5 . left-margin))
@end example

  If no specific base offset is set for alignment, it is always relative
to the left edge of the text area.  For example, @samp{:align-to 0} in a
header-line aligns with the first text column in the text area.

  A value of the form @code{(@var{num} . @var{expr})} stands for the
product of the values of @var{num} and @var{expr}.  For example,
@code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
@var{image})} specifies half the width (or height) of the specified
image.

  The form @code{(+ @var{expr} ...)} adds up the value of the
expressions.  The form @code{(- @var{expr} ...)} negates or subtracts
the value of the expressions.

@node Other Display Specs
@subsection Other Display Specifications

  Here are the other sorts of display specifications that you can use
in the @code{display} text property.

@table @code
@item @var{string}
Display @var{string} instead of the text that has this property.

Recursive display specifications are not supported---@var{string}'s
@code{display} properties, if any, are not used.

@item (image . @var{image-props})
This kind of display specification is an image descriptor (@pxref{Images}).
When used as a display specification, it means to display the image
instead of the text that has the display specification.

@item (slice @var{x} @var{y} @var{width} @var{height})
This specification together with @code{image} specifies a @dfn{slice}
(a partial area) of the image to display.  The elements @var{y} and
@var{x} specify the top left corner of the slice, within the image;
@var{width} and @var{height} specify the width and height of the
slice.  Integers are numbers of pixels.  A floating-point number
in the range 0.0--1.0 stands for that fraction of the width or height
of the entire image.

@item ((margin nil) @var{string})
A display specification of this form means to display @var{string}
instead of the text that has the display specification, at the same
position as that text.  It is equivalent to using just @var{string},
but it is done as a special case of marginal display (@pxref{Display
Margins}).

@item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
@itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
This display specification on any character of a line of text causes
the specified @var{bitmap} be displayed in the left or right fringes
for that line, instead of the characters that have the display
specification.  The optional @var{face} specifies the colors to be
used for the bitmap.  @xref{Fringe Bitmaps}, for the details.

@item (space-width @var{factor})
This display specification affects all the space characters within the
text that has the specification.  It displays all of these spaces
@var{factor} times as wide as normal.  The element @var{factor} should
be an integer or float.  Characters other than spaces are not affected
at all; in particular, this has no effect on tab characters.

@item (height @var{height})
This display specification makes the text taller or shorter.
Here are the possibilities for @var{height}:

@table @asis
@item @code{(+ @var{n})}
@c FIXME: Add an index for "step"?  --xfq
This means to use a font that is @var{n} steps larger.  A ``step'' is
defined by the set of available fonts---specifically, those that match
what was otherwise specified for this text, in all attributes except
height.  Each size for which a suitable font is available counts as
another step.  @var{n} should be an integer.

@item @code{(- @var{n})}
This means to use a font that is @var{n} steps smaller.

@item a number, @var{factor}
A number, @var{factor}, means to use a font that is @var{factor} times
as tall as the default font.

@item a symbol, @var{function}
A symbol is a function to compute the height.  It is called with the
current height as argument, and should return the new height to use.

@item anything else, @var{form}
If the @var{height} value doesn't fit the previous possibilities, it is
a form.  Emacs evaluates it to get the new height, with the symbol
@code{height} bound to the current specified font height.
@end table

@item (raise @var{factor})
This kind of display specification raises or lowers the text
it applies to, relative to the baseline of the line.

@var{factor} must be a number, which is interpreted as a multiple of the
height of the affected text.  If it is positive, that means to display
the characters raised.  If it is negative, that means to display them
lower down.

If the text also has a @code{height} display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
@end table

@c We put all the `@code{(when ...)}' on one line to encourage
@c makeinfo's end-of-sentence heuristics to DTRT.  Previously, the dot
@c was at eol; the info file ended up w/ two spaces rendered after it.
  You can make any display specification conditional.  To do that,
package it in another list of the form
@code{(when @var{condition} . @var{spec})}.
Then the specification @var{spec} applies only when
@var{condition} evaluates to a non-@code{nil} value.  During the
evaluation, @code{object} is bound to the string or buffer having the
conditional @code{display} property.  @code{position} and
@code{buffer-position} are bound to the position within @code{object}
and the buffer position where the @code{display} property was found,
respectively.  Both positions can be different when @code{object} is a
string.

@node Display Margins
@subsection Displaying in the Margins
@cindex display margins
@cindex margins, display

  A buffer can have blank areas called @dfn{display margins} on the
left and on the right.  Ordinary text never appears in these areas,
but you can put things into the display margins using the
@code{display} property.  There is currently no way to make text or
images in the margin mouse-sensitive.

  The way to display something in the margins is to specify it in a
margin display specification in the @code{display} property of some
text.  This is a replacing display specification, meaning that the
text you put it on does not get displayed; the margin display appears,
but that text does not.

  A margin display specification looks like @code{((margin
right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
Here, @var{spec} is another display specification that says what to
display in the margin.  Typically it is a string of text to display,
or an image descriptor.

  To display something in the margin @emph{in association with}
certain buffer text, without altering or preventing the display of
that text, put a @code{before-string} property on the text and put the
margin display specification on the contents of the before-string.

  Before the display margins can display anything, you must give
them a nonzero width.  The usual way to do that is to set these
variables:

@defvar left-margin-width
This variable specifies the width of the left margin, in character
cell (a.k.a.@: ``column'') units.  It is buffer-local in all buffers.
A value of @code{nil} means no left marginal area.
@end defvar

@defvar right-margin-width
This variable specifies the width of the right margin, in character
cell units.  It is buffer-local in all buffers.  A value of @code{nil}
means no right marginal area.
@end defvar

  Setting these variables does not immediately affect the window.  These
variables are checked when a new buffer is displayed in the window.
Thus, you can make changes take effect by calling
@code{set-window-buffer}.

  You can also set the margin widths immediately.

@defun set-window-margins window left &optional right
This function specifies the margin widths for window @var{window}, in
character cell units.  The argument @var{left} controls the left
margin, and @var{right} controls the right margin (default @code{0}).
@end defun

@defun window-margins &optional window
This function returns the width of the left and right margins of
@var{window} as a cons cell of the form @w{@code{(@var{left}
. @var{right})}}.  If one of the two marginal areas does not exist,
its width is returned as @code{nil}; if neither of the two margins exist,
the function returns @code{(nil)}.  If @var{window} is @code{nil}, the
selected window is used.
@end defun

@node Images
@section Images
@cindex images in buffers

  To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the @code{display}
property of text that is displayed (@pxref{Display Property}).

  Emacs is usually able to display images when it is run on a
graphical terminal.  Images cannot be displayed in a text terminal, on
certain graphical terminals that lack the support for this, or if
Emacs is compiled without image support.  You can use the function
@code{display-images-p} to determine if images can in principle be
displayed (@pxref{Display Feature Testing}).

@menu
* Image Formats::       Supported image formats.
* Image Descriptors::   How to specify an image for use in @code{:display}.
* XBM Images::          Special features for XBM format.
* XPM Images::          Special features for XPM format.
* PostScript Images::   Special features for PostScript format.
* ImageMagick Images::  Special features available through ImageMagick.
* Other Image Types::   Various other formats are supported.
* Defining Images::     Convenient ways to define an image for later use.
* Showing Images::      Convenient ways to display an image once it is defined.
* Multi-Frame Images::  Some images contain more than one frame.
* Image Cache::         Internal mechanisms of image display.
@end menu

@node Image Formats
@subsection Image Formats
@cindex image formats
@cindex image types

  Emacs can display a number of different image formats.  Some of
these image formats are supported only if particular support libraries
are installed.  On some platforms, Emacs can load support libraries on
demand; if so, the variable @code{dynamic-library-alist} can be used
to modify the set of known names for these dynamic libraries.
@xref{Dynamic Libraries}.

  Supported image formats (and the required support libraries) include
PBM and XBM (which do not depend on support libraries and are always
available), XPM (@code{libXpm}), GIF (@code{libgif} or
@code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
(@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).

  Each of these image formats is associated with an @dfn{image type
symbol}.  The symbols for the above formats are, respectively,
@code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
@code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.

  Furthermore, if you build Emacs with ImageMagick
(@code{libMagickWand}) support, Emacs can display any image format
that ImageMagick can.  @xref{ImageMagick Images}.  All images
displayed via ImageMagick have type symbol @code{imagemagick}.

@defvar image-types
This variable contains a list of type symbols for image formats which
are potentially supported in the current configuration.

``Potentially'' means that Emacs knows about the image types, not
necessarily that they can be used (for example, they could depend on
unavailable dynamic libraries).  To know which image types are really
available, use @code{image-type-available-p}.
@end defvar

@defun image-type-available-p type
This function returns non-@code{nil} if images of type @var{type} can
be loaded and displayed.  @var{type} must be an image type symbol.

For image types whose support libraries are statically linked, this
function always returns @code{t}.  For image types whose support
libraries are dynamically loaded, it returns @code{t} if the library
could be loaded and @code{nil} otherwise.
@end defun

@node Image Descriptors
@subsection Image Descriptors
@cindex image descriptor

  An @dfn{image descriptor} is a list which specifies the underlying
data for an image, and how to display it.  It is typically used as the
value of a @code{display} overlay or text property (@pxref{Other
Display Specs}); but @xref{Showing Images}, for convenient helper
functions to insert images into buffers.

  Each image descriptor has the form @code{(image . @var{props})},
where @var{props} is a property list of alternating keyword symbols
and values, including at least the pair @code{:type @var{type}} that
specifies the image type.

  The following is a list of properties that are meaningful for all
image types (there are also properties which are meaningful only for
certain image types, as documented in the following subsections):

@table @code
@item :type @var{type}
The image type.
@ifnottex
@xref{Image Formats}.
@end ifnottex
Every image descriptor must include this property.

@item :file @var{file}
This says to load the image from file @var{file}.  If @var{file} is
not an absolute file name, it is expanded in @code{data-directory}.

@item :data @var{data}
This specifies the raw image data.  Each image descriptor must have
either @code{:data} or @code{:file}, but not both.

For most image types, the value of a @code{:data} property should be a
string containing the image data.  Some image types do not support
@code{:data}; for some others, @code{:data} alone is not enough, so
you need to use other image properties along with @code{:data}.  See
the following subsections for details.

@item :margin @var{margin}
This specifies how many pixels to add as an extra margin around the
image.  The value, @var{margin}, must be a non-negative number, or a
pair @code{(@var{x} . @var{y})} of such numbers.  If it is a pair,
@var{x} specifies how many pixels to add horizontally, and @var{y}
specifies how many pixels to add vertically.  If @code{:margin} is not
specified, the default is zero.

@item :ascent @var{ascent}
This specifies the amount of the image's height to use for its
ascent---that is, the part above the baseline.  The value,
@var{ascent}, must be a number in the range 0 to 100, or the symbol
@code{center}.

If @var{ascent} is a number, that percentage of the image's height is
used for its ascent.

If @var{ascent} is @code{center}, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.

If this property is omitted, it defaults to 50.

@item :relief @var{relief}
This adds a shadow rectangle around the image.  The value,
@var{relief}, specifies the width of the shadow lines, in pixels.  If
@var{relief} is negative, shadows are drawn so that the image appears
as a pressed button; otherwise, it appears as an unpressed button.

@item :conversion @var{algorithm}
This specifies a conversion algorithm that should be applied to the
image before it is displayed; the value, @var{algorithm}, specifies
which algorithm.

@table @code
@item laplace
@itemx emboss
Specifies the Laplace edge detection algorithm, which blurs out small
differences in color while highlighting larger differences.  People
sometimes consider this useful for displaying the image for a
``disabled'' button.

@item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
@cindex edge detection, images
Specifies a general edge-detection algorithm.  @var{matrix} must be
either a nine-element list or a nine-element vector of numbers.  A pixel
at position @math{x/y} in the transformed image is computed from
original pixels around that position.  @var{matrix} specifies, for each
pixel in the neighborhood of @math{x/y}, a factor with which that pixel
will influence the transformed pixel; element @math{0} specifies the
factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
the pixel at @math{x/y-1} etc., as shown below:
@iftex
@tex
$$\pmatrix{x-1/y-1 & x/y-1  & x+1/y-1 \cr
   x-1/y  &   x/y &    x+1/y \cr
   x-1/y+1&   x/y+1 &  x+1/y+1 \cr}$$
@end tex
@end iftex
@ifnottex
@display
  (x-1/y-1  x/y-1  x+1/y-1
   x-1/y    x/y    x+1/y
   x-1/y+1  x/y+1  x+1/y+1)
@end display
@end ifnottex

The resulting pixel is computed from the color intensity of the color
resulting from summing up the RGB values of surrounding pixels,
multiplied by the specified factors, and dividing that sum by the sum
of the factors' absolute values.

Laplace edge-detection currently uses a matrix of
@iftex
@tex
$$\pmatrix{1 & 0 & 0 \cr
   0&  0 &  0 \cr
   0 & 0 & -1 \cr}$$
@end tex
@end iftex
@ifnottex
@display
  (1  0  0
   0  0  0
   0  0 -1)
@end display
@end ifnottex

Emboss edge-detection uses a matrix of
@iftex
@tex
$$\pmatrix{ 2 & -1 &  0 \cr
   -1 &  0 &  1 \cr
    0  & 1 & -2 \cr}$$
@end tex
@end iftex
@ifnottex
@display
  ( 2 -1  0
   -1  0  1
    0  1 -2)
@end display
@end ifnottex

@item disabled
Specifies transforming the image so that it looks ``disabled''.
@end table

@item :mask @var{mask}
If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
a clipping mask for the image, so that the background of a frame is
visible behind the image.  If @var{bg} is not specified, or if @var{bg}
is @code{t}, determine the background color of the image by looking at
the four corners of the image, assuming the most frequently occurring
color from the corners is the background color of the image.  Otherwise,
@var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
specifying the color to assume for the background of the image.

If @var{mask} is @code{nil}, remove a mask from the image, if it has
one.  Images in some formats include a mask which can be removed by
specifying @code{:mask nil}.

@item :pointer @var{shape}
This specifies the pointer shape when the mouse pointer is over this
image.  @xref{Pointer Shape}, for available pointer shapes.

@item :map @var{map}
@cindex image maps
This associates an image map of @dfn{hot spots} with this image.

An image map is an alist where each element has the format
@code{(@var{area} @var{id} @var{plist})}.  An @var{area} is specified
as either a rectangle, a circle, or a polygon.

A rectangle is a cons
@code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
which specifies the pixel coordinates of the upper left and bottom right
corners of the rectangle area.

A circle is a cons
@code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
which specifies the center and the radius of the circle; @var{r} may
be a float or integer.

A polygon is a cons
@code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
where each pair in the vector describes one corner in the polygon.

When the mouse pointer lies on a hot-spot area of an image, the
@var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
property, that defines a tool-tip for the hot-spot, and if it contains
a @code{pointer} property, that defines the shape of the mouse cursor when
it is on the hot-spot.
@xref{Pointer Shape}, for available pointer shapes.

When you click the mouse when the mouse pointer is over a hot-spot, an
event is composed by combining the @var{id} of the hot-spot with the
mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
@var{id} is @code{area4}.
@end table

@defun image-mask-p spec &optional frame
This function returns @code{t} if image @var{spec} has a mask bitmap.
@var{frame} is the frame on which the image will be displayed.
@var{frame} @code{nil} or omitted means to use the selected frame
(@pxref{Input Focus}).
@end defun

@node XBM Images
@subsection XBM Images
@cindex XBM

  To use XBM format, specify @code{xbm} as the image type.  This image
format doesn't require an external library, so images of this type are
always supported.

  Additional image properties supported for the @code{xbm} image type are:

@table @code
@item :foreground @var{foreground}
The value, @var{foreground}, should be a string specifying the image
foreground color, or @code{nil} for the default color.  This color is
used for each pixel in the XBM that is 1.  The default is the frame's
foreground color.

@item :background @var{background}
The value, @var{background}, should be a string specifying the image
background color, or @code{nil} for the default color.  This color is
used for each pixel in the XBM that is 0.  The default is the frame's
background color.
@end table

  If you specify an XBM image using data within Emacs instead of an
external file, use the following three properties:

@table @code
@item :data @var{data}
The value, @var{data}, specifies the contents of the image.
There are three formats you can use for @var{data}:

@itemize @bullet
@item
A vector of strings or bool-vectors, each specifying one line of the
image.  Do specify @code{:height} and @code{:width}.

@item
A string containing the same byte sequence as an XBM file would contain.
You must not specify @code{:height} and @code{:width} in this case,
because omitting them is what indicates the data has the format of an
XBM file.  The file contents specify the height and width of the image.

@item
A string or a bool-vector containing the bits of the image (plus perhaps
some extra bits at the end that will not be used).  It should contain at
least @var{width} * @code{height} bits.  In this case, you must specify
@code{:height} and @code{:width}, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the
size of the image.
@end itemize

@item :width @var{width}
The value, @var{width}, specifies the width of the image, in pixels.

@item :height @var{height}
The value, @var{height}, specifies the height of the image, in pixels.
@end table

@node XPM Images
@subsection XPM Images
@cindex XPM

  To use XPM format, specify @code{xpm} as the image type.  The
additional image property @code{:color-symbols} is also meaningful with
the @code{xpm} image type:

@table @code
@item :color-symbols @var{symbols}
The value, @var{symbols}, should be an alist whose elements have the
form @code{(@var{name} . @var{color})}.  In each element, @var{name} is
the name of a color as it appears in the image file, and @var{color}
specifies the actual color to use for displaying that name.
@end table

@node PostScript Images
@subsection PostScript Images
@cindex postscript images

  To use PostScript for an image, specify image type @code{postscript}.
This works only if you have Ghostscript installed.  You must always use
these three properties:

@table @code
@item :pt-width @var{width}
The value, @var{width}, specifies the width of the image measured in
points (1/72 inch).  @var{width} must be an integer.

@item :pt-height @var{height}
The value, @var{height}, specifies the height of the image in points
(1/72 inch).  @var{height} must be an integer.

@item :bounding-box @var{box}
The value, @var{box}, must be a list or vector of four integers, which
specifying the bounding box of the PostScript image, analogous to the
@samp{BoundingBox} comment found in PostScript files.

@example
%%BoundingBox: 22 171 567 738
@end example
@end table

@node ImageMagick Images
@subsection ImageMagick Images
@cindex ImageMagick images
@cindex images, support for more formats

  If you build Emacs with ImageMagick support, you can use the
ImageMagick library to load many image formats (@pxref{File
Conveniences,,, emacs, The GNU Emacs Manual}).  The image type symbol
for images loaded via ImageMagick is @code{imagemagick}, regardless of
the actual underlying image format.

@defun imagemagick-types
This function returns a list of image file extensions supported by the
current ImageMagick installation.  Each list element is a symbol
representing an internal ImageMagick name for an image type, such as
@code{BMP} for @file{.bmp} images.
@end defun

@defopt imagemagick-enabled-types
The value of this variable is a list of ImageMagick image types which
Emacs may attempt to render using ImageMagick.  Each list element
should be one of the symbols in the list returned by
@code{imagemagick-types}, or an equivalent string.  Alternatively, a
value of @code{t} enables ImageMagick for all possible image types.
Regardless of the value of this variable,
@code{imagemagick-types-inhibit} (see below) takes precedence.
@end defopt

@defopt imagemagick-types-inhibit
The value of this variable lists the ImageMagick image types which
should never be rendered using ImageMagick, regardless of the value of
@code{imagemagick-enabled-types}.  A value of @code{t} disables
ImageMagick entirely.
@end defopt

@defvar image-format-suffixes
This variable is an alist mapping image types to file name extensions.
Emacs uses this in conjunction with the @code{:format} image property
(see below) to give a hint to the ImageMagick library as to the type
of an image.  Each element has the form @code{(@var{type}
@var{extension})}, where @var{type} is a symbol specifying an image
content-type, and @var{extension} is a string that specifies the
associated file name extension.
@end defvar

  Images loaded with ImageMagick support the following additional
image descriptor properties:

@table @code
@item :background @var{background}
@var{background}, if non-@code{nil}, should be a string specifying a
color, which is used as the image's background color if the image
supports transparency.  If the value is @code{nil}, it defaults to the
frame's background color.

@item :width @var{width}, :height @var{height}
The @code{:width} and @code{:height} keywords are used for scaling the
image.  If only one of them is specified, the other one will be
calculated so as to preserve the aspect ratio.  If both are specified,
aspect ratio may not be preserved.

@item :max-width @var{max-width}, :max-height @var{max-height}
The @code{:max-width} and @code{:max-height} keywords are used for
scaling if the size of the image of the image exceeds these values.
If @code{:width} is set it will have precedence over @code{max-width},
and if @code{:height} is set it will have precedence over
@code{max-height}, but you can otherwise mix these keywords as you
wish.  @code{:max-width} and @code{:max-height} will always preserve
the aspect ratio.

@item :format @var{type}
The value, @var{type}, should be a symbol specifying the type of the
image data, as found in @code{image-format-suffixes}.  This is used
when the image does not have an associated file name, to provide a
hint to ImageMagick to help it detect the image type.

@item :rotation @var{angle}
Specifies a rotation angle in degrees.

@item :index @var{frame}
@c Doesn't work: http://debbugs.gnu.org/7978
@xref{Multi-Frame Images}.
@end table

@node Other Image Types
@subsection Other Image Types
@cindex PBM

  For PBM images, specify image type @code{pbm}.  Color, gray-scale and
monochromatic images are supported.   For mono PBM images, two additional
image properties are supported.

@table @code
@item :foreground @var{foreground}
The value, @var{foreground}, should be a string specifying the image
foreground color, or @code{nil} for the default color.  This color is
used for each pixel in the PBM that is 1.  The default is the frame's
foreground color.

@item :background @var{background}
The value, @var{background}, should be a string specifying the image
background color, or @code{nil} for the default color.  This color is
used for each pixel in the PBM that is 0.  The default is the frame's
background color.
@end table

@noindent
The remaining image types that Emacs can support are:

@table @asis
@item GIF
Image type @code{gif}.
Supports the @code{:index} property.  @xref{Multi-Frame Images}.

@item JPEG
Image type @code{jpeg}.

@item PNG
Image type @code{png}.

@item SVG
Image type @code{svg}.

@item TIFF
Image type @code{tiff}.
Supports the @code{:index} property.  @xref{Multi-Frame Images}.
@end table

@node Defining Images
@subsection Defining Images
@cindex define image

  The functions @code{create-image}, @code{defimage} and
@code{find-image} provide convenient ways to create image descriptors.

@defun create-image file-or-data &optional type data-p &rest props
This function creates and returns an image descriptor which uses the
data in @var{file-or-data}.  @var{file-or-data} can be a file name or
a string containing the image data; @var{data-p} should be @code{nil}
for the former case, non-@code{nil} for the latter case.

The optional argument @var{type} is a symbol specifying the image type.
If @var{type} is omitted or @code{nil}, @code{create-image} tries to
determine the image type from the file's first few bytes, or else
from the file's name.

The remaining arguments, @var{props}, specify additional image
properties---for example,

@c ':heuristic-mask' is not documented?
@example
(create-image "foo.xpm" 'xpm nil :heuristic-mask t)
@end example

The function returns @code{nil} if images of this type are not
supported.  Otherwise it returns an image descriptor.
@end defun

@defmac defimage symbol specs &optional doc
This macro defines @var{symbol} as an image name.  The arguments
@var{specs} is a list which specifies how to display the image.
The third argument, @var{doc}, is an optional documentation string.

Each argument in @var{specs} has the form of a property list, and each
one should specify at least the @code{:type} property and either the
@code{:file} or the @code{:data} property.  The value of @code{:type}
should be a symbol specifying the image type, the value of
@code{:file} is the file to load the image from, and the value of
@code{:data} is a string containing the actual image data.  Here is an
example:

@example
(defimage test-image
  ((:type xpm :file "~/test1.xpm")
   (:type xbm :file "~/test1.xbm")))
@end example

@code{defimage} tests each argument, one by one, to see if it is
usable---that is, if the type is supported and the file exists.  The
first usable argument is used to make an image descriptor which is
stored in @var{symbol}.

If none of the alternatives will work, then @var{symbol} is defined
as @code{nil}.
@end defmac

@defun find-image specs
This function provides a convenient way to find an image satisfying one
of a list of image specifications @var{specs}.

Each specification in @var{specs} is a property list with contents
depending on image type.  All specifications must at least contain the
properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
the image type, e.g., @code{xbm}, @var{file} is the file to load the
image from, and @var{data} is a string containing the actual image data.
The first specification in the list whose @var{type} is supported, and
@var{file} exists, is used to construct the image specification to be
returned.  If no specification is satisfied, @code{nil} is returned.

The image is looked for in @code{image-load-path}.
@end defun

@defvar image-load-path
This variable's value is a list of locations in which to search for
image files.  If an element is a string or a variable symbol whose
value is a string, the string is taken to be the name of a directory
to search.  If an element is a variable symbol whose value is a list,
that is taken to be a list of directory names to search.

The default is to search in the @file{images} subdirectory of the
directory specified by @code{data-directory}, then the directory
specified by @code{data-directory}, and finally in the directories in
@code{load-path}.  Subdirectories are not automatically included in
the search, so if you put an image file in a subdirectory, you have to
supply the subdirectory name explicitly.  For example, to find the
image @file{images/foo/bar.xpm} within @code{data-directory}, you
should specify the image as follows:

@example
(defimage foo-image '((:type xpm :file "foo/bar.xpm")))
@end example
@end defvar

@defun image-load-path-for-library library image &optional path no-error
This function returns a suitable search path for images used by the
Lisp package @var{library}.

The function searches for @var{image} first using @code{image-load-path},
excluding @file{@code{data-directory}/images}, and then in
@code{load-path}, followed by a path suitable for @var{library}, which
includes @file{../../etc/images} and @file{../etc/images} relative to
the library file itself, and finally in
@file{@code{data-directory}/images}.

Then this function returns a list of directories which contains first
the directory in which @var{image} was found, followed by the value of
@code{load-path}.  If @var{path} is given, it is used instead of
@code{load-path}.

If @var{no-error} is non-@code{nil} and a suitable path can't be
found, don't signal an error.  Instead, return a list of directories as
before, except that @code{nil} appears in place of the image directory.

Here is an example of using @code{image-load-path-for-library}:

@example
(defvar image-load-path) ; shush compiler
(let* ((load-path (image-load-path-for-library
                    "mh-e" "mh-logo.xpm"))
       (image-load-path (cons (car load-path)
                              image-load-path)))
  (mh-tool-bar-folder-buttons-init))
@end example
@end defun

@node Showing Images
@subsection Showing Images
@cindex show image

  You can use an image descriptor by setting up the @code{display}
property yourself, but it is easier to use the functions in this
section.

@defun insert-image image &optional string area slice
This function inserts @var{image} in the current buffer at point.  The
value @var{image} should be an image descriptor; it could be a value
returned by @code{create-image}, or the value of a symbol defined with
@code{defimage}.  The argument @var{string} specifies the text to put
in the buffer to hold the image.  If it is omitted or @code{nil},
@code{insert-image} uses @code{" "} by default.

The argument @var{area} specifies whether to put the image in a margin.
If it is @code{left-margin}, the image appears in the left margin;
@code{right-margin} specifies the right margin.  If @var{area} is
@code{nil} or omitted, the image is displayed at point within the
buffer's text.

The argument @var{slice} specifies a slice of the image to insert.  If
@var{slice} is @code{nil} or omitted the whole image is inserted.
Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
@var{height})} which specifies the @var{x} and @var{y} positions and
@var{width} and @var{height} of the image area to insert.  Integer
values are in units of pixels.  A floating-point number in the range
0.0--1.0 stands for that fraction of the width or height of the entire
image.

Internally, this function inserts @var{string} in the buffer, and gives
it a @code{display} property which specifies @var{image}.  @xref{Display
Property}.
@end defun

@cindex slice, image
@cindex image slice
@defun insert-sliced-image image &optional string area rows cols
This function inserts @var{image} in the current buffer at point, like
@code{insert-image}, but splits the image into @var{rows}x@var{cols}
equally sized slices.

If an image is inserted ``sliced'', Emacs displays each slice as a
separate image, and allow more intuitive scrolling up/down, instead of
jumping up/down the entire image when paging through a buffer that
displays (large) images.
@end defun

@defun put-image image pos &optional string area
This function puts image @var{image} in front of @var{pos} in the
current buffer.  The argument @var{pos} should be an integer or a
marker.  It specifies the buffer position where the image should appear.
The argument @var{string} specifies the text that should hold the image
as an alternative to the default.

The argument @var{image} must be an image descriptor, perhaps returned
by @code{create-image} or stored by @code{defimage}.

The argument @var{area} specifies whether to put the image in a margin.
If it is @code{left-margin}, the image appears in the left margin;
@code{right-margin} specifies the right margin.  If @var{area} is
@code{nil} or omitted, the image is displayed at point within the
buffer's text.

Internally, this function creates an overlay, and gives it a
@code{before-string} property containing text that has a @code{display}
property whose value is the image.  (Whew!)
@end defun

@defun remove-images start end &optional buffer
This function removes images in @var{buffer} between positions
@var{start} and @var{end}.  If @var{buffer} is omitted or @code{nil},
images are removed from the current buffer.

This removes only images that were put into @var{buffer} the way
@code{put-image} does it, not images that were inserted with
@code{insert-image} or in other ways.
@end defun

@defun image-size spec &optional pixels frame
@cindex size of image
This function returns the size of an image as a pair
@w{@code{(@var{width} . @var{height})}}.  @var{spec} is an image
specification.  @var{pixels} non-@code{nil} means return sizes
measured in pixels, otherwise return sizes measured in canonical
character units (fractions of the width/height of the frame's default
font).  @var{frame} is the frame on which the image will be displayed.
@var{frame} null or omitted means use the selected frame (@pxref{Input
Focus}).
@end defun

@defvar max-image-size
This variable is used to define the maximum size of image that Emacs
will load.  Emacs will refuse to load (and display) any image that is
larger than this limit.

If the value is an integer, it directly specifies the maximum
image height and width, measured in pixels.  If it is floating
point, it specifies the maximum image height and width
as a ratio to the frame height and width.  If the value is
non-numeric, there is no explicit limit on the size of images.

The purpose of this variable is to prevent unreasonably large images
from accidentally being loaded into Emacs.  It only takes effect the
first time an image is loaded.  Once an image is placed in the image
cache, it can always be displayed, even if the value of
@code{max-image-size} is subsequently changed (@pxref{Image Cache}).
@end defvar

@node Multi-Frame Images
@subsection Multi-Frame Images
@cindex multi-frame images

@cindex animation
@cindex image animation
@cindex image frames
Some image files can contain more than one image.  We say that there
are multiple ``frames'' in the image.  At present, Emacs supports
multiple frames for GIF, TIFF, and certain ImageMagick formats such as
DJVM@.

The frames can be used either to represent multiple ``pages'' (this is
usually the case with multi-frame TIFF files, for example), or to
create animation (usually the case with multi-frame GIF files).

A multi-frame image has a property @code{:index}, whose value is an
integer (counting from 0) that specifies which frame is being displayed.

@defun image-multi-frame-p image
This function returns non-@code{nil} if @var{image} contains more than
one frame.  The actual return value is a cons @code{(@var{nimages}
. @var{delay})}, where @var{nimages} is the number of frames and
@var{delay} is the delay in seconds between them, or @code{nil}
if the image does not specify a delay.  Images that are intended to be
animated usually specify a frame delay, whereas ones that are intended
to be treated as multiple pages do not.
@end defun

@defun image-current-frame image
This function returns the index of the current frame number for
@var{image}, counting from 0.
@end defun

@defun image-show-frame image n &optional nocheck
This function switches @var{image} to frame number @var{n}.  It
replaces a frame number outside the valid range with that of the end
of the range, unless @var{nocheck} is non-@code{nil}.  If @var{image}
does not contain a frame with the specified number, the image displays
as a hollow box.
@end defun

@defun image-animate image &optional index limit
This function animates @var{image}.  The optional integer @var{index}
specifies the frame from which to start (default 0).  The optional
argument @var{limit} controls the length of the animation.  If omitted
or @code{nil}, the image animates once only; if @code{t} it loops
forever; if a number animation stops after that many seconds.
@end defun

@vindex image-minimum-frame-delay
@vindex image-default-frame-delay
@noindent Animation operates by means of a timer.  Note that Emacs imposes a
minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
If the image itself does not specify a delay, Emacs uses
@code{image-default-frame-delay}.

@defun image-animate-timer image
This function returns the timer responsible for animating @var{image},
if there is one.
@end defun


@node Image Cache
@subsection Image Cache
@cindex image cache

  Emacs caches images so that it can display them again more
efficiently.  When Emacs displays an image, it searches the image
cache for an existing image specification @code{equal} to the desired
specification.  If a match is found, the image is displayed from the
cache.  Otherwise, Emacs loads the image normally.

@defun image-flush spec &optional frame
This function removes the image with specification @var{spec} from the
image cache of frame @var{frame}.  Image specifications are compared
using @code{equal}.  If @var{frame} is @code{nil}, it defaults to the
selected frame.  If @var{frame} is @code{t}, the image is flushed on
all existing frames.

In Emacs's current implementation, each graphical terminal possesses an
image cache, which is shared by all the frames on that terminal
(@pxref{Multiple Terminals}).  Thus, refreshing an image in one frame
also refreshes it in all other frames on the same terminal.
@end defun

  One use for @code{image-flush} is to tell Emacs about a change in an
image file.  If an image specification contains a @code{:file}
property, the image is cached based on the file's contents when the
image is first displayed.  Even if the file subsequently changes,
Emacs continues displaying the old version of the image.  Calling
@code{image-flush} flushes the image from the cache, forcing Emacs to
re-read the file the next time it needs to display that image.

  Another use for @code{image-flush} is for memory conservation.  If
your Lisp program creates a large number of temporary images over a
period much shorter than @code{image-cache-eviction-delay} (see
below), you can opt to flush unused images yourself, instead of
waiting for Emacs to do it automatically.

@defun clear-image-cache &optional filter
This function clears an image cache, removing all the images stored in
it.  If @var{filter} is omitted or @code{nil}, it clears the cache for
the selected frame.  If @var{filter} is a frame, it clears the cache
for that frame.  If @var{filter} is @code{t}, all image caches are
cleared.  Otherwise, @var{filter} is taken to be a file name, and all
images associated with that file name are removed from all image
caches.
@end defun

If an image in the image cache has not been displayed for a specified
period of time, Emacs removes it from the cache and frees the
associated memory.

@defvar image-cache-eviction-delay
This variable specifies the number of seconds an image can remain in
the cache without being displayed.  When an image is not displayed for
this length of time, Emacs removes it from the image cache.

Under some circumstances, if the number of images in the cache grows
too large, the actual eviction delay may be shorter than this.

If the value is @code{nil}, Emacs does not remove images from the cache
except when you explicitly clear it.  This mode can be useful for
debugging.
@end defvar

@node Buttons
@section Buttons
@cindex buttons in buffers
@cindex clickable buttons in buffers

  The Button package defines functions for inserting and manipulating
@dfn{buttons} that can be activated with the mouse or via keyboard
commands.  These buttons are typically used for various kinds of
hyperlinks.

  A button is essentially a set of text or overlay properties,
attached to a stretch of text in a buffer.  These properties are
called @dfn{button properties}.  One of these properties, the
@dfn{action property}, specifies a function which is called when the
user invokes the button using the keyboard or the mouse.  The action
function may examine the button and use its other properties as
desired.

  In some ways, the Button package duplicates the functionality in the
Widget package.  @xref{Top, , Introduction, widget, The Emacs Widget
Library}.  The advantage of the Button package is that it is faster,
smaller, and simpler to program.  From the point of view of the user,
the interfaces produced by the two packages are very similar.

@menu
* Button Properties::      Button properties with special meanings.
* Button Types::           Defining common properties for classes of buttons.
* Making Buttons::         Adding buttons to Emacs buffers.
* Manipulating Buttons::   Getting and setting properties of buttons.
* Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
@end menu

@node Button Properties
@subsection Button Properties
@cindex button properties

  Each button has an associated list of properties defining its
appearance and behavior, and other arbitrary properties may be used
for application specific purposes.  The following properties have
special meaning to the Button package:

@table @code
@item action
@kindex action @r{(button property)}
The function to call when the user invokes the button, which is passed
the single argument @var{button}.  By default this is @code{ignore},
which does nothing.

@item mouse-action
@kindex mouse-action @r{(button property)}
This is similar to @code{action}, and when present, will be used
instead of @code{action} for button invocations resulting from
mouse-clicks (instead of the user hitting @key{RET}).  If not
present, mouse-clicks use @code{action} instead.

@item face
@kindex face @r{(button property)}
This is an Emacs face controlling how buttons of this type are
displayed; by default this is the @code{button} face.

@item mouse-face
@kindex mouse-face @r{(button property)}
This is an additional face which controls appearance during
mouse-overs (merged with the usual button face); by default this is
the usual Emacs @code{highlight} face.

@item keymap
@kindex keymap @r{(button property)}
The button's keymap, defining bindings active within the button
region.  By default this is the usual button region keymap, stored
in the variable @code{button-map}, which defines @key{RET} and
@key{mouse-2} to invoke the button.

@item type
@kindex type @r{(button property)}
The button type.  @xref{Button Types}.

@item help-echo
@kindex help-index @r{(button property)}
A string displayed by the Emacs tool-tip help system; by default,
@code{"mouse-2, RET: Push this button"}.

@item follow-link
@kindex follow-link @r{(button property)}
The follow-link property, defining how a @key{Mouse-1} click behaves
on this button, @xref{Clickable Text}.

@item button
@kindex button @r{(button property)}
All buttons have a non-@code{nil} @code{button} property, which may be useful
in finding regions of text that comprise buttons (which is what the
standard button functions do).
@end table

  There are other properties defined for the regions of text in a
button, but these are not generally interesting for typical uses.

@node Button Types
@subsection Button Types
@cindex button types

  Every button has a @dfn{button type}, which defines default values
for the button's properties.  Button types are arranged in a
hierarchy, with specialized types inheriting from more general types,
so that it's easy to define special-purpose types of buttons for
specific tasks.

@defun define-button-type name &rest properties
Define a `button type' called @var{name} (a symbol).
The remaining arguments
form a sequence of @var{property value} pairs, specifying default
property values for buttons with this type (a button's type may be set
by giving it a @code{type} property when creating the button, using
the @code{:type} keyword argument).

In addition, the keyword argument @code{:supertype} may be used to
specify a button-type from which @var{name} inherits its default
property values.  Note that this inheritance happens only when
@var{name} is defined; subsequent changes to a supertype are not
reflected in its subtypes.
@end defun

  Using @code{define-button-type} to define default properties for
buttons is not necessary---buttons without any specified type use the
built-in button-type @code{button}---but it is encouraged, since
doing so usually makes the resulting code clearer and more efficient.

@node Making Buttons
@subsection Making Buttons
@cindex making buttons

  Buttons are associated with a region of text, using an overlay or
text properties to hold button-specific information, all of which are
initialized from the button's type (which defaults to the built-in
button type @code{button}).  Like all Emacs text, the appearance of
the button is governed by the @code{face} property; by default (via
the @code{face} property inherited from the @code{button} button-type)
this is a simple underline, like a typical web-page link.

  For convenience, there are two sorts of button-creation functions,
those that add button properties to an existing region of a buffer,
called @code{make-...button}, and those that also insert the button
text, called @code{insert-...button}.

  The button-creation functions all take the @code{&rest} argument
@var{properties}, which should be a sequence of @var{property value}
pairs, specifying properties to add to the button; see @ref{Button
Properties}.  In addition, the keyword argument @code{:type} may be
used to specify a button-type from which to inherit other properties;
see @ref{Button Types}.  Any properties not explicitly specified
during creation will be inherited from the button's type (if the type
defines such a property).

  The following functions add a button using an overlay
(@pxref{Overlays}) to hold the button properties:

@defun make-button beg end &rest properties
This makes a button from @var{beg} to @var{end} in the
current buffer, and returns it.
@end defun

@defun insert-button label &rest properties
This insert a button with the label @var{label} at point,
and returns it.
@end defun

  The following functions are similar, but using text properties
(@pxref{Text Properties}) to hold the button properties.  Such buttons
do not add markers to the buffer, so editing in the buffer does not
slow down if there is an extremely large numbers of buttons.  However,
if there is an existing face text property on the text (e.g., a face
assigned by Font Lock mode), the button face may not be visible.  Both
of these functions return the starting position of the new button.

@defun make-text-button beg end &rest properties
This makes a button from @var{beg} to @var{end} in the current buffer,
using text properties.
@end defun

@defun insert-text-button label &rest properties
This inserts a button with the label @var{label} at point, using text
properties.
@end defun

@node Manipulating Buttons
@subsection Manipulating Buttons
@cindex manipulating buttons

These are functions for getting and setting properties of buttons.
Often these are used by a button's invocation function to determine
what to do.

Where a @var{button} parameter is specified, it means an object
referring to a specific button, either an overlay (for overlay
buttons), or a buffer-position or marker (for text property buttons).
Such an object is passed as the first argument to a button's
invocation function when it is invoked.

@defun button-start button
Return the position at which @var{button} starts.
@end defun

@defun button-end button
Return the position at which @var{button} ends.
@end defun

@defun button-get button prop
Get the property of button @var{button} named @var{prop}.
@end defun

@defun button-put button prop val
Set @var{button}'s @var{prop} property to @var{val}.
@end defun

@defun button-activate button &optional use-mouse-action
Call @var{button}'s @code{action} property (i.e., invoke the function
that is the value of that property, passing it the single argument
@var{button}).  If @var{use-mouse-action} is non-@code{nil}, try to
invoke the button's @code{mouse-action} property instead of
@code{action}; if the button has no @code{mouse-action} property, use
@code{action} as normal.
@end defun

@defun button-label button
Return @var{button}'s text label.
@end defun

@defun button-type button
Return @var{button}'s button-type.
@end defun

@defun button-has-type-p button type
Return @code{t} if @var{button} has button-type @var{type}, or one of
@var{type}'s subtypes.
@end defun

@defun button-at pos
Return the button at position @var{pos} in the current buffer, or
@code{nil}.  If the button at @var{pos} is a text property button, the
return value is a marker pointing to @var{pos}.
@end defun

@defun button-type-put type prop val
Set the button-type @var{type}'s @var{prop} property to @var{val}.
@end defun

@defun button-type-get type prop
Get the property of button-type @var{type} named @var{prop}.
@end defun

@defun button-type-subtype-p type supertype
Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
@end defun

@node Button Buffer Commands
@subsection Button Buffer Commands
@cindex button buffer commands

These are commands and functions for locating and operating on
buttons in an Emacs buffer.

@code{push-button} is the command that a user uses to actually `push'
a button, and is bound by default in the button itself to @key{RET}
and to @key{mouse-2} using a local keymap in the button's overlay or
text properties.  Commands that are useful outside the buttons itself,
such as @code{forward-button} and @code{backward-button} are
additionally available in the keymap stored in
@code{button-buffer-map}; a mode which uses buttons may want to use
@code{button-buffer-map} as a parent keymap for its keymap.

If the button has a non-@code{nil} @code{follow-link} property, and
@code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
will also activate the @code{push-button} command.
@xref{Clickable Text}.

@deffn Command push-button &optional pos use-mouse-action
Perform the action specified by a button at location @var{pos}.
@var{pos} may be either a buffer position or a mouse-event.  If
@var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
mouse-event (@pxref{Mouse Events}), try to invoke the button's
@code{mouse-action} property instead of @code{action}; if the button
has no @code{mouse-action} property, use @code{action} as normal.
@var{pos} defaults to point, except when @code{push-button} is invoked
interactively as the result of a mouse-event, in which case, the mouse
event's position is used.  If there's no button at @var{pos}, do
nothing and return @code{nil}, otherwise return @code{t}.
@end deffn

@deffn Command forward-button n &optional wrap display-message
Move to the @var{n}th next button, or @var{n}th previous button if
@var{n} is negative.  If @var{n} is zero, move to the start of any
button at point.  If @var{wrap} is non-@code{nil}, moving past either
end of the buffer continues from the other end.  If
@var{display-message} is non-@code{nil}, the button's help-echo string
is displayed.  Any button with a non-@code{nil} @code{skip} property
is skipped over.  Returns the button found.
@end deffn

@deffn Command backward-button n &optional wrap display-message
Move to the @var{n}th previous button, or @var{n}th next button if
@var{n} is negative.  If @var{n} is zero, move to the start of any
button at point.  If @var{wrap} is non-@code{nil}, moving past either
end of the buffer continues from the other end.  If
@var{display-message} is non-@code{nil}, the button's help-echo string
is displayed.  Any button with a non-@code{nil} @code{skip} property
is skipped over.  Returns the button found.
@end deffn

@defun next-button pos &optional count-current
@defunx previous-button pos &optional count-current
Return the next button after (for @code{next-button}) or before (for
@code{previous-button}) position @var{pos} in the current buffer.  If
@var{count-current} is non-@code{nil}, count any button at @var{pos}
in the search, instead of starting at the next button.
@end defun

@node Abstract Display
@section Abstract Display
@cindex ewoc
@cindex display, abstract
@cindex display, arbitrary objects
@cindex model/view/controller
@cindex view part, model/view/controller

  The Ewoc package constructs buffer text that represents a structure
of Lisp objects, and updates the text to follow changes in that
structure.  This is like the ``view'' component in the
``model/view/controller'' design paradigm.  Ewoc means ``Emacs's
Widget for Object Collections''.

  An @dfn{ewoc} is a structure that organizes information required to
construct buffer text that represents certain Lisp data.  The buffer
text of the ewoc has three parts, in order: first, fixed @dfn{header}
text; next, textual descriptions of a series of data elements (Lisp
objects that you specify); and last, fixed @dfn{footer} text.
Specifically, an ewoc contains information on:

@itemize @bullet
@item
The buffer which its text is generated in.

@item
The text's start position in the buffer.

@item
The header and footer strings.

@item
@cindex node, ewoc
@c or "@cindex node, abstract display"?
A doubly-linked chain of @dfn{nodes}, each of which contains:

@itemize
@item
A @dfn{data element}, a single Lisp object.

@item
Links to the preceding and following nodes in the chain.
@end itemize

@item
A @dfn{pretty-printer} function which is responsible for
inserting the textual representation of a data
element value into the current buffer.
@end itemize

  Typically, you define an ewoc with @code{ewoc-create}, and then pass
the resulting ewoc structure to other functions in the Ewoc package to
build nodes within it, and display it in the buffer.  Once it is
displayed in the buffer, other functions determine the correspondence
between buffer positions and nodes, move point from one node's textual
representation to another, and so forth.  @xref{Abstract Display
Functions}.

@cindex encapsulation, ewoc
@c or "@cindex encapsulation, abstract display"?
  A node @dfn{encapsulates} a data element much the way a variable
holds a value.  Normally, encapsulation occurs as a part of adding a
node to the ewoc.  You can retrieve the data element value and place a
new value in its place, like so:

@lisp
(ewoc-data @var{node})
@result{} value

(ewoc-set-data @var{node} @var{new-value})
@result{} @var{new-value}
@end lisp

@noindent
You can also use, as the data element value, a Lisp object (list or
vector) that is a container for the ``real'' value, or an index into
some other structure.  The example (@pxref{Abstract Display Example})
uses the latter approach.

  When the data changes, you will want to update the text in the
buffer.  You can update all nodes by calling @code{ewoc-refresh}, or
just specific nodes using @code{ewoc-invalidate}, or all nodes
satisfying a predicate using @code{ewoc-map}.  Alternatively, you can
delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
and add new nodes in their place.  Deleting a node from an ewoc deletes
its associated textual description from buffer, as well.

@menu
* Abstract Display Functions::  Functions in the Ewoc package.
* Abstract Display Example::    Example of using Ewoc.
@end menu

@node Abstract Display Functions
@subsection Abstract Display Functions

  In this subsection, @var{ewoc} and @var{node} stand for the
structures described above (@pxref{Abstract Display}), while
@var{data} stands for an arbitrary Lisp object used as a data element.

@defun ewoc-create pretty-printer &optional header footer nosep
This constructs and returns a new ewoc, with no nodes (and thus no data
elements).  @var{pretty-printer} should be a function that takes one
argument, a data element of the sort you plan to use in this ewoc, and
inserts its textual description at point using @code{insert} (and never
@code{insert-before-markers}, because that would interfere with the
Ewoc package's internal mechanisms).

Normally, a newline is automatically inserted after the header,
the footer and every node's textual description.  If @var{nosep}
is non-@code{nil}, no newline is inserted.  This may be useful for
displaying an entire ewoc on a single line, for example, or for
making nodes ``invisible'' by arranging for @var{pretty-printer}
to do nothing for those nodes.

An ewoc maintains its text in the buffer that is current when
you create it, so switch to the intended buffer before calling
@code{ewoc-create}.
@end defun

@defun ewoc-buffer ewoc
This returns the buffer where @var{ewoc} maintains its text.
@end defun

@defun ewoc-get-hf ewoc
This returns a cons cell @code{(@var{header} . @var{footer})}
made from @var{ewoc}'s header and footer.
@end defun

@defun ewoc-set-hf ewoc header footer
This sets the header and footer of @var{ewoc} to the strings
@var{header} and @var{footer}, respectively.
@end defun

@defun ewoc-enter-first ewoc data
@defunx ewoc-enter-last ewoc data
These add a new node encapsulating @var{data}, putting it, respectively,
at the beginning or end of @var{ewoc}'s chain of nodes.
@end defun

@defun ewoc-enter-before ewoc node data
@defunx ewoc-enter-after ewoc node data
These add a new node encapsulating @var{data}, adding it to
@var{ewoc} before or after @var{node}, respectively.
@end defun

@defun ewoc-prev ewoc node
@defunx ewoc-next ewoc node
These return, respectively, the previous node and the next node of @var{node}
in @var{ewoc}.
@end defun

@defun ewoc-nth ewoc n
This returns the node in @var{ewoc} found at zero-based index @var{n}.
A negative @var{n} means count from the end.  @code{ewoc-nth} returns
@code{nil} if @var{n} is out of range.
@end defun

@defun ewoc-data node
This extracts the data encapsulated by @var{node} and returns it.
@end defun

@defun ewoc-set-data node data
This sets the data encapsulated by @var{node} to @var{data}.
@end defun

@defun ewoc-locate ewoc &optional pos guess
This determines the node in @var{ewoc} which contains point (or
@var{pos} if specified), and returns that node.  If @var{ewoc} has no
nodes, it returns @code{nil}.  If @var{pos} is before the first node,
it returns the first node; if @var{pos} is after the last node, it returns
the last node.  The optional third arg @var{guess}
should be a node that is likely to be near @var{pos}; this doesn't
alter the result, but makes the function run faster.
@end defun

@defun ewoc-location node
This returns the start position of @var{node}.
@end defun

@defun ewoc-goto-prev ewoc arg
@defunx ewoc-goto-next ewoc arg
These move point to the previous or next, respectively, @var{arg}th node
in @var{ewoc}.  @code{ewoc-goto-prev} does not move if it is already at
the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
moves past the last node, returning @code{nil}.  Excepting this special
case, these functions return the node moved to.
@end defun

@defun ewoc-goto-node ewoc node
This moves point to the start of @var{node} in @var{ewoc}.
@end defun

@defun ewoc-refresh ewoc
This function regenerates the text of @var{ewoc}.  It works by
deleting the text between the header and the footer, i.e., all the
data elements' representations, and then calling the pretty-printer
function for each node, one by one, in order.
@end defun

@defun ewoc-invalidate ewoc &rest nodes
This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
@var{ewoc} are updated instead of the entire set.
@end defun

@defun ewoc-delete ewoc &rest nodes
This deletes each node in @var{nodes} from @var{ewoc}.
@end defun

@defun ewoc-filter ewoc predicate &rest args
This calls @var{predicate} for each data element in @var{ewoc} and
deletes those nodes for which @var{predicate} returns @code{nil}.
Any @var{args} are passed to @var{predicate}.
@end defun

@defun ewoc-collect ewoc predicate &rest args
This calls @var{predicate} for each data element in @var{ewoc}
and returns a list of those elements for which @var{predicate}
returns non-@code{nil}.  The elements in the list are ordered
as in the buffer.  Any @var{args} are passed to @var{predicate}.
@end defun

@defun ewoc-map map-function ewoc &rest args
This calls @var{map-function} for each data element in @var{ewoc} and
updates those nodes for which @var{map-function} returns non-@code{nil}.
Any @var{args} are passed to @var{map-function}.
@end defun

@node Abstract Display Example
@subsection Abstract Display Example

  Here is a simple example using functions of the ewoc package to
implement a ``color components display'', an area in a buffer that
represents a vector of three integers (itself representing a 24-bit RGB
value) in various ways.

@example
(setq colorcomp-ewoc nil
      colorcomp-data nil
      colorcomp-mode-map nil
      colorcomp-labels ["Red" "Green" "Blue"])

(defun colorcomp-pp (data)
  (if data
      (let ((comp (aref colorcomp-data data)))
        (insert (aref colorcomp-labels data) "\t: #x"
                (format "%02X" comp) " "
                (make-string (ash comp -2) ?#) "\n"))
    (let ((cstr (format "#%02X%02X%02X"
                        (aref colorcomp-data 0)
                        (aref colorcomp-data 1)
                        (aref colorcomp-data 2)))
          (samp " (sample text) "))
      (insert "Color\t: "
              (propertize samp 'face
                          `(foreground-color . ,cstr))
              (propertize samp 'face
                          `(background-color . ,cstr))
              "\n"))))

(defun colorcomp (color)
  "Allow fiddling with COLOR in a new buffer.
The buffer is in Color Components mode."
  (interactive "sColor (name or #RGB or #RRGGBB): ")
  (when (string= "" color)
    (setq color "green"))
  (unless (color-values color)
    (error "No such color: %S" color))
  (switch-to-buffer
   (generate-new-buffer (format "originally: %s" color)))
  (kill-all-local-variables)
  (setq major-mode 'colorcomp-mode
        mode-name "Color Components")
  (use-local-map colorcomp-mode-map)
  (erase-buffer)
  (buffer-disable-undo)
  (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
                                     (color-values color))))
        (ewoc (ewoc-create 'colorcomp-pp
                           "\nColor Components\n\n"
                           (substitute-command-keys
                            "\n\\@{colorcomp-mode-map@}"))))
    (set (make-local-variable 'colorcomp-data) data)
    (set (make-local-variable 'colorcomp-ewoc) ewoc)
    (ewoc-enter-last ewoc 0)
    (ewoc-enter-last ewoc 1)
    (ewoc-enter-last ewoc 2)
    (ewoc-enter-last ewoc nil)))
@end example

@cindex controller part, model/view/controller
  This example can be extended to be a ``color selection widget'' (in
other words, the controller part of the ``model/view/controller''
design paradigm) by defining commands to modify @code{colorcomp-data}
and to ``finish'' the selection process, and a keymap to tie it all
together conveniently.

@smallexample
(defun colorcomp-mod (index limit delta)
  (let ((cur (aref colorcomp-data index)))
    (unless (= limit cur)
      (aset colorcomp-data index (+ cur delta)))
    (ewoc-invalidate
     colorcomp-ewoc
     (ewoc-nth colorcomp-ewoc index)
     (ewoc-nth colorcomp-ewoc -1))))

(defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
(defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
(defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
(defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
(defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
(defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))

(defun colorcomp-copy-as-kill-and-exit ()
  "Copy the color components into the kill ring and kill the buffer.
The string is formatted #RRGGBB (hash followed by six hex digits)."
  (interactive)
  (kill-new (format "#%02X%02X%02X"
                    (aref colorcomp-data 0)
                    (aref colorcomp-data 1)
                    (aref colorcomp-data 2)))
  (kill-buffer nil))

(setq colorcomp-mode-map
      (let ((m (make-sparse-keymap)))
        (suppress-keymap m)
        (define-key m "i" 'colorcomp-R-less)
        (define-key m "o" 'colorcomp-R-more)
        (define-key m "k" 'colorcomp-G-less)
        (define-key m "l" 'colorcomp-G-more)
        (define-key m "," 'colorcomp-B-less)
        (define-key m "." 'colorcomp-B-more)
        (define-key m " " 'colorcomp-copy-as-kill-and-exit)
        m))
@end smallexample

Note that we never modify the data in each node, which is fixed when the
ewoc is created to be either @code{nil} or an index into the vector
@code{colorcomp-data}, the actual color components.

@node Blinking
@section 括弧を点滅する
@cindex 対応する括弧
@cindex 釣り合った括弧
@cindex 閉じ括弧

本節では、ユーザーが閉じ括弧を挿入したときに
Emacsが対応する開き括弧を指し示す機構について述べます。

@defvar blink-paren-function
この変数の値は、閉じ括弧構文の文字が挿入されるたびに
呼び出される（引数なしの）関数であること。
@code{blink-paren-function}の値が@code{nil}であると、なにもしない。
@end defvar

@defopt blink-matching-paren
この変数が@code{nil}であると、@code{blink-matching-open}はなにもしない。
@end defopt

@defopt blink-matching-paren-distance
この変数は、対応する括弧の走査を諦めるまでの最大距離を指定する。
@end defopt

@defopt blink-matching-delay
この関数は、対応する括弧にカーソルを留める秒数を指定する。
秒未満を指定してもしばしば結果は良好であるが、
デフォルトはすべてのシステムで動作する1である。
@end defopt

@deffn Command blink-matching-open
この関数は、@code{blink-paren-function}のデフォルト値である。
閉じ括弧構文の文字のうしろにポイントがあることを仮定し、
カーソルを対応する開き括弧へ一時的に移動する。
その文字がスクリーン上になければ、
その文字が現れる文脈をエコー領域に表示する。
遅れが大きくならないように、
@code{blink-matching-paren-distance}文字より離れては探さない。

つぎは、この関数を明示的に呼び出す例である。

@smallexample
@group
(defun interactive-blink-matching-open ()
  "Indicate momentarily the start of parenthesized sexp before point."
  (interactive)
@end group
@group
  (let ((blink-matching-paren-distance
         (buffer-size))
        (blink-matching-paren t))
    (blink-matching-open)))
@end group
@end smallexample
@end deffn

@node Character Display
@section Character Display

  This section describes how characters are actually displayed by
Emacs.  Typically, a character is displayed as a @dfn{glyph} (a
graphical symbol which occupies one character position on the screen),
whose appearance corresponds to the character itself.  For example,
the character @samp{a} (character code 97) is displayed as @samp{a}.
Some characters, however, are displayed specially.  For example, the
formfeed character (character code 12) is usually displayed as a
sequence of two glyphs, @samp{^L}, while the newline character
(character code 10) starts a new screen line.

  You can modify how each character is displayed by defining a
@dfn{display table}, which maps each character code into a sequence of
glyphs.  @xref{Display Tables}.

@menu
* Usual Display::       The usual conventions for displaying characters.
* Display Tables::      What a display table consists of.
* Active Display Table::  How Emacs selects a display table to use.
* Glyphs::              How to define a glyph, and what glyphs mean.
* Glyphless Chars::     How glyphless characters are drawn.
@end menu

@node Usual Display
@subsection 通常の画面表示慣習

以下に、各文字符号を（表示テーブル
@iftex
（@pxref{Display Tables}）
@end iftex
@ifnottex
@end ifnottex
がない場合に）表示する方法を述べます。
表示テーブルがある場合はそちらが優先されます。

@cindex printable ASCII characters
@itemize @bullet
@item
The @dfn{printable @acronym{ASCII} characters}, character codes 32
through 126 (consisting of numerals, English letters, and symbols like
@samp{#}) are displayed literally.

@item
The tab character (character code 9) displays as whitespace stretching
up to the next tab stop column.  @xref{Text Display,,, emacs, The GNU
Emacs Manual}.  The variable @code{tab-width} controls the number of
spaces per tab stop (see below).

@item
The newline character (character code 10) has a special effect: it
ends the preceding line and starts a new line.

@cindex ASCII control characters
@item
表示できない@dfn{@acronym{ASCII}制御文字}---文字符号0から31と
@key{DEL}文字（文字符号127）---は、
@code{ctl-arrow}の値に従って2つの表示方法の一方を使う。
この変数が@code{nil}（デフォルト値）以外であると、
これらのコードを2つの字形列に対応付け、
最初の字形は@samp{^}である。
（表示テーブルで@samp{^}の代わりに使う字形を指定できる。）
例えば、@key{DEL}文字は@samp{^?}のように表示される。

@code{ctl-arrow}が@code{nil}ならば、これらの文字は８進数エスケープで
表示される（下記参照）。

このルールは、改行（文字符号13）文字がバッファに現れた場合も適用される。
ただし、通常、改行はバッファテキストに現れない。これらは行末変換
によって消去される（@pxref{Coding System Basics}）。

@cindex octal escapes
@item
@dfn{生バイト}は、文字コード128から255の非@acronym{ASCII}文字である
（@pxref{Text Representations}）。
これらの文字は@dfn{８進数エスケープ}、すなわちと4つの字形列
（最初の字形は@samp{\}の@acronym{ASCII}コードで、残りの３字形は
文字コードを８進数で代表）。
（表示テーブルで@samp{\}のかわりに使う字形を指定できる。）

@item
Each non-@acronym{ASCII} character with code above 255 is displayed
literally, if the terminal supports it.  If the terminal does not
support it, the character is said to be @dfn{glyphless}, and it is
usually displayed using a placeholder glyph.  For example, if a
graphical terminal has no font for a character, Emacs usually displays
a box containing the character code in hexadecimal.  @xref{Glyphless
Chars}.
@end itemize

これらの表示慣習は、いかなる文字においても、
その文字に対するアクティブな表示テーブルにおいて、その文字の項目が@code{nil}であっても
適用されます。
したがって、表示テーブルを設定するときには、
特別なふるまいをさせたい文字だけを指定すればよいのです。

これらの変数は、特定の文字群のスクリーンへの表示方法に影響します。
これらは文字が占めるコラム数を変化させるので、
字下げ関数にも影響します。
これらの変数は、モード行の表示方法にも影響します。
新たな値を用いてモード行の再表示を強制したいときには、
関数@code{force-mode-line-update}（@pxref{Mode Line Format}）を
呼び出します。

@defopt ctl-arrow
@cindex コントロール文字の表示
このバッファローカルな変数は、
コントロール文字の表示方法を制御する。
@code{nil}以外であると、@samp{^A}のように
カレットに続けて文字を表示する。
@code{nil}であると、@samp{\001}のように
バックスラッシュに続けて3桁の8進数字で表示する。
@end defopt

@defopt tab-width
この変数の値は、Emacsのバッファ内のタブ文字の表示に使う
タブストップの間隔である。
値はカラム単位で指定し、デフォルトは8である。
この機能は、コマンド@code{tab-to-tab-stop}で設定する
ユーザー設定可能なタブストップとはまったく独立であることに注意する。
@xref{Indent Tabs}。
@end defopt

@node Display Tables
@subsection Display Tables

@cindex display table
表示テーブルは、実際にはサブタイプが@code{display-table}である
特殊用途の文字テーブル（@pxref{Char-Tables}）で、実際の文字の表示慣習より
優先されます。本節では、表示テーブルオブジェクトの作成・検査・要素の
割当方法を説明します。

@defun make-display-table
表示テーブルを作成して返す。
テーブルのすべての要素の初期値は@code{nil}である。
@end defun

表示テーブルの通常の要素は、文字コードでインデックスされます。
インデックス@var{c}の要素は、文字コード@var{c}の表示方法を指定します。
要素の値は@code{nil}である
（すなわち、文字@var{c}を通常の方法で表示する、@pxref{Usual Display}）か、
字形コードのベクトル（文字@var{c}をその字形で表示する。@pxref{Glyphs}）
になります。

@strong{警告：} 表示テーブルを使って改行文字の表示を変更すると、
バッファ全体は長い1つの『行』として表示されます。

表示テーブルには6つの『追加スロット』もあり、
それらは特別な目的を果たします。
それらの意味をつぎに示します。
スロットの内容が@code{nil}であると、
そのスロットに対して以下に述べる
デフォルトを使うことを意味します。

@table @asis
@item 0
切り詰めたスクリーン行の末尾に使う字形
（デフォルトは@samp{$}）。@xref{Glyphs}。
On graphical terminals, Emacs uses
arrows in the fringes to indicate truncation, so the display table has
no effect.

@item 1
継続している行の末尾に使う字形
（デフォルトは@samp{\}）。
On graphical terminals, Emacs uses curved arrows in the fringes to
indicate continuation, so the display table has no effect.

@item 2
文字を8進数文字コードで表示したことを表す字形
（デフォルトは@samp{\}）。

@item 3
コントロール文字を表す字形
（デフォルトは@samp{^}）。

@item 4
不可視な行があることを表す字形のベクトル（デフォルトは@samp{...}）。
@xref{Selective Display}。

@item 5
左右に隣り合ったウィンドウの境界に使う字形
（デフォルトは@samp{|}）。
@xref{Splitting Windows}。
This takes effect only
when there are no scroll bars; if scroll bars are supported and in use,
a scroll bar separates the two windows.
@end table

たとえば、@code{ctl-arrow}に@code{nil}以外の値を設定した効果を
模倣する表示テーブルの作成方法をつぎに示します。
(@pxref{Glyphs}, for the function @code{make-glyph-code}):

@example
(setq disptab (make-display-table))
(dotimes (i 32)
  (or (= i ?\t)
      (= i ?\n)
      (aset disptab i
            (vector (make-glyph-code ?^ 'escape-glyph)
                    (make-glyph-code (+ i 64) 'escape-glyph)))))
(aset disptab 127
      (vector (make-glyph-code ?^ 'escape-glyph)
              (make-glyph-code ?? 'escape-glyph)))))
@end example

@defun display-table-slot display-table slot
この関数は表示テーブル@var{display-table}の
追加スロット@var{slot}の値を返す。
引数@var{slot}は0から5までの数であるか、
スロット名（シンボル）であること。
正しいシンボルは、@code{truncation}、@code{wrap}、
@code{escape}、@code{control}、@code{selective-display}、
@code{vertical-border}である。
@end defun

@defun set-display-table-slot display-table slot value
この関数は表示テーブル@var{display-table}の
追加スロット@var{slot}に値@var{value}を保存する。
引数@var{slot}は0から5までの数であるか、
スロット名（シンボル）であること。
正しいシンボルは、@code{truncation}、@code{wrap}、
@code{escape}、@code{control}、@code{selective-display}、
@code{vertical-border}である。
@end defun

@defun describe-display-table display-table
This function displays a description of the display table
@var{display-table} in a help buffer.
@end defun

@deffn Command describe-current-display-table
This command displays a description of the current display table in a
help buffer.
@end deffn

@node Active Display Table
@subsection Active Display Table
@cindex active display table

各ウィンドウに表示テーブルを指定でき、
各バッファにも表示テーブルを指定できます。
各ウィンドウの表示テーブルは、（存在するならば）バッファの表示テーブルより優先されます。
両表とも存在しない場合は、Emacsは標準表示テーブルを使います。
それが@code{nil}の場合は、Emacsは通常の文字の表示を行います(@pxref{Usual Display})。

表示テーブルは、モード行の表示方法にも影響します。
新たな表示テーブルを用いてモード行の再表示を強制したいときには、
関数@code{force-mode-line-update}（@pxref{Mode Line Format}）を
呼び出します。

@defun window-display-table &optional window
この関数は、ウィンドウ@var{window}の表示テーブルを返す。
@var{window}に表示テーブルが割り付けられていなければ@code{nil}を返す。
@end defun

@defun set-window-display-table window table
この関数は、ウィンドウ@var{window}の表示テーブルとして
@var{table}を設定する。
引数@var{table}は、表示テーブルであるか@code{nil}であること。
@end defun

@defvar buffer-display-table
この変数はすべてのバッファで自動的にバッファローカルである。
バッファでの値は、そのバッファに対して用いる表示テーブルを指定する。
それが@code{nil}であると、バッファに表示テーブルを
割り付けていないことを意味する。
@end defvar

@defvar standard-display-table
この変数の値はデフォルトの表示テーブルであり、
ウィンドウに表示テーブルがなく
そのウィンドウのバッファにも表示テーブルがない場合に使われる。
この変数はデフォルトでは@code{nil}である。
@end defvar

The @file{disp-table} library defines several functions for changing
the standard display table.

@node Glyphs
@subsection Glyphs
@cindex glyph

@cindex glyph code
  A @dfn{glyph} is a graphical symbol which occupies a single
character position on the screen.  Each glyph is represented in Lisp
as a @dfn{glyph code}, which specifies a character and optionally a
face to display it in (@pxref{Faces}).  The main use of glyph codes is
as the entries of display tables (@pxref{Display Tables}).  The
following functions are used to manipulate glyph codes:

@defun make-glyph-code char &optional face
This function returns a glyph code representing char @var{char} with
face @var{face}.  If @var{face} is omitted or @code{nil}, the glyph
uses the default face; in that case, the glyph code is an integer.  If
@var{face} is non-@code{nil}, the glyph code is not necessarily an
integer object.
@end defun

@defun glyph-char glyph
This function returns the character of glyph code @var{glyph}.
@end defun

@defun glyph-face glyph
This function returns face of glyph code @var{glyph}, or @code{nil} if
@var{glyph} uses the default face.
@end defun

@ifnottex
  You can set up a @dfn{glyph table} to change how glyph codes are
actually displayed on text terminals.  This feature is semi-obsolete;
use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).

@defvar glyph-table
この変数の値は（@code{nil}でないならば）、現在の字形テーブルを示す。
It takes effect only on character terminals; on graphical
displays, all glyphs are displayed literally.
これは、@var{g}番目の要素が、字形コード@var{g}を定義する、ベクトルであること。
字形コード@var{g}のフェイスは未定義である。
各要素は以下のいずれかになる。

@table @asis
@item @code{nil}
Display this glyph literally.
グリフをそのまま画面に表示する。

@item a string
この字形を出力するために端末へ指定された文字列を送出する。

@item a glyph code
指定された字形コードを表示する。
@end table

字形コード（整数）が字形テーブルの長さに等しいか大きいと、
そのコードは単純に表示されます。
@end defvar
@end ifnottex

@node Glyphless Chars
@subsection Glyphless Character Display
@cindex glyphless characters

  @dfn{Glyphless characters} are characters which are displayed in a
special way, e.g., as a box containing a hexadecimal code, instead of
being displayed literally.  These include characters which are
explicitly defined to be glyphless, as well as characters for which
there is no available font (on a graphical display), and characters
which cannot be encoded by the terminal's coding system (on a text
terminal).

@defvar glyphless-char-display
The value of this variable is a char-table which defines glyphless
characters and how they are displayed.  Each entry must be one of the
following display methods:

@table @asis
@item @code{nil}
Display the character in the usual way.

@item @code{zero-width}
Don't display the character.

@item @code{thin-space}
Display a thin space, 1-pixel wide on graphical displays, or
1-character wide on text terminals.

@item @code{empty-box}
Display an empty box.

@item @code{hex-code}
Display a box containing the Unicode codepoint of the character, in
hexadecimal notation.

@item an @acronym{ASCII} string
Display a box containing that string.

@item a cons cell @code{(@var{graphical} . @var{text})}
Display with @var{graphical} on graphical displays, and with
@var{text} on text terminals.  Both @var{graphical} and @var{text}
must be one of the display methods described above.
@end table

@noindent
The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
@acronym{ASCII} string display methods are drawn with the
@code{glyphless-char} face.

The char-table has one extra slot, which determines how to display any
character that cannot be displayed with any available font, or cannot
be encoded by the terminal's coding system.  Its value should be one
of the above display methods, except @code{zero-width} or a cons cell.

If a character has a non-@code{nil} entry in an active display table,
the display table takes effect; in this case, Emacs does not consult
@code{glyphless-char-display} at all.
@end defvar

@defopt glyphless-char-display-control
This user option provides a convenient way to set
@code{glyphless-char-display} for groups of similar characters.  Do
not set its value directly from Lisp code; the value takes effect only
via a custom @code{:set} function (@pxref{Variable Definitions}),
which updates @code{glyphless-char-display}.

Its value should be an alist of elements @code{(@var{group}
. @var{method})}, where @var{group} is a symbol specifying a group of
characters, and @var{method} is a symbol specifying how to display
them.

@var{group} should be one of the following:

@table @code
@item c0-control
@acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
excluding the newline and tab characters (normally displayed as escape
sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
emacs, The GNU Emacs Manual}).

@item c1-control
Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
@code{U+009F} (normally displayed as octal escape sequences like
@samp{\230}).

@item format-control
Characters of Unicode General Category `Cf', such as @samp{U+200E}
(Left-to-Right Mark), but excluding characters that have graphic
images, such as @samp{U+00AD} (Soft Hyphen).

@item no-font
Characters for there is no suitable font, or which cannot be encoded
by the terminal's coding system.
@end table

@c FIXME: this can also be `acronym', but that's not currently
@c completely implemented; it applies only to the format-control
@c group, and only works if the acronym is in `char-acronym-table'.
The @var{method} symbol should be one of @code{zero-width},
@code{thin-space}, @code{empty-box}, or @code{hex-code}.  These have
the same meanings as in @code{glyphless-char-display}, above.
@end defopt

@node Beeping
@section ベルを鳴らす
@cindex ベルを鳴らす

本節では、ユーザーの注意を引くためにEmacsにベルを鳴らせる
（あるいはスクリーンを点滅させる）方法について述べます。
ベルを鳴らす頻度はなるべく控えめにしてください。
頻繁にベルが鳴るとわずらわしいものです。
エラーを通知するほうがふさわしいときには、
単にベルを鳴らさないように注意してください。
（@pxref{Errors}。）

@defun ding &optional do-not-terminate
@cindex キーボードマクロの終了
この関数は、ベルを鳴らすかスクリーンを点滅する
（下記の@code{visible-bell}を参照）。
また、@var{do-not-terminate}が@code{nil}であると
現在実行中のキーボードマクロを終了する。
@end defun

@defun beep &optional do-not-terminate
@code{ding}の同義語。
@end defun

@defopt visible-bell
この変数は、ベルを鳴らすかわりにスクリーンを点滅させるかどうかを決定する。
@code{nil}以外であると点滅するを意味し、
@code{nil}であると点滅しないを意味する。
これは、グラフィック表示を用いている場合か、
端末のtermcapの定義にビジュアルベル機能（@samp{vb}）がある
文字端末で有効である。
@end defopt

@defvar ring-bell-function
これが@code{nil}以外であると、
Emacsに『ベルを鳴らす』方法を指定する。
この値は、引数なしの関数であること。
If this is
non-@code{nil}, it takes precedence over the @code{visible-bell}
variable.
@end defvar

@node Window Systems
@section ウィンドウシステム

  Emacs works with several window systems, most notably the X Window
System.  Both Emacs and X use the term ``window'', but use it
differently.  An Emacs frame is a single window as far as X is
concerned; the individual Emacs windows are not known to X at all.
Emacsはいくつかのウィンドウシステムで、
特にXウィンドウシステムで動作します。
EmacsもXも用語『ウィンドウ』を使いますが、用法は異なります。
Emacsの1つのフレームは、Xでは1つのウィンドウです。
Emacsの個々のウィンドウについては、Xはまったくわかりません。

@defvar window-system
This terminal-local variable tells Lisp programs what window system
Emacs is using for displaying the frame.  The possible values are
この変数は、Emacsが動作しているウィンドウシステムの種類を
Lispプログラムに伝える。
可能な値はつぎのとおりである。

@table @code
@item x
@cindex X Window System
Xウィンドウシステムを用いて表示している。
@item w32
Emacs is displaying the frame using native MS-Windows GUI.
MS-Windows GUI を用いて表示している。
@item ns
Emacs is displaying the frame using the Nextstep interface (used on
GNUstep and Mac OS X).
@item pc
MS-DOSの直接画面描画を用いてフレームを表示している。
@item nil
文字ベースの端末を用いてフレームを表示している。
@end table
@end defvar

@defvar initial-window-system
This variable holds the value of @code{window-system} used for the
first frame created by Emacs during startup.  (When Emacs is invoked
with the @option{--daemon} option, it does not create any initial
frames, so @code{initial-window-system} is @code{nil}, except on
MS-Windows, where it is still @code{w32}.  @xref{Initial Options,
daemon,, emacs, The GNU Emacs Manual}.)
@end defvar

@defun window-system &optional frame
This function returns a symbol whose name tells what window system is
used for displaying @var{frame} (which defaults to the currently
selected frame).  The list of possible symbols it returns is the same
one documented for the variable @code{window-system} above.
@end defun

  Do @emph{not} use @code{window-system} and
@code{initial-window-system} as predicates or boolean flag variables,
if you want to write code that works differently on text terminals and
graphic displays.  That is because @code{window-system} is not a good
indicator of Emacs capabilities on a given display type.  Instead, use
@code{display-graphic-p} or any of the other @code{display-*-p}
predicates described in @ref{Display Feature Testing}.

@node Bidirectional Display
@section Bidirectional Display
@cindex bidirectional display
@cindex right-to-left text

  Emacs can display text written in scripts, such as Arabic, Farsi,
and Hebrew, whose natural ordering for horizontal text display runs
from right to left.  Furthermore, segments of Latin script and digits
embedded in right-to-left text are displayed left-to-right, while
segments of right-to-left script embedded in left-to-right text
(e.g., Arabic or Hebrew text in comments or strings in a program
source file) are appropriately displayed right-to-left.  We call such
mixtures of left-to-right and right-to-left text @dfn{bidirectional
text}.  This section describes the facilities and options for editing
and displaying bidirectional text.

@cindex logical order
@cindex reading order
@cindex visual order
@cindex unicode bidirectional algorithm
@cindex UBA
@cindex bidirectional reordering
@cindex reordering, of bidirectional text
  Text is stored in Emacs buffers and strings in @dfn{logical} (or
@dfn{reading}) order, i.e., the order in which a human would read
each character.  In right-to-left and bidirectional text, the order in
which characters are displayed on the screen (called @dfn{visual
order}) is not the same as logical order; the characters' screen
positions do not increase monotonically with string or buffer
position.  In performing this @dfn{bidirectional reordering}, Emacs
follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
which is described in Annex #9 of the Unicode standard
(@url{http://www.unicode.org/reports/tr9/}).  Emacs provides a ``Full
Bidirectionality'' class implementation of the @acronym{UBA},
consistent with the requirements of the Unicode Standard v7.0.

@defvar bidi-display-reordering
If the value of this buffer-local variable is non-@code{nil} (the
default), Emacs performs bidirectional reordering for display.  The
reordering affects buffer text, as well as display strings and overlay
strings from text and overlay properties in the buffer (@pxref{Overlay
Properties}, and @pxref{Display Property}).  If the value is
@code{nil}, Emacs does not perform bidirectional reordering in the
buffer.

The default value of @code{bidi-display-reordering} controls the
reordering of strings which are not directly supplied by a buffer,
including the text displayed in mode lines (@pxref{Mode Line Format})
and header lines (@pxref{Header Lines}).
@end defvar

@cindex unibyte buffers, and bidi reordering
  Emacs never reorders the text of a unibyte buffer, even if
@code{bidi-display-reordering} is non-@code{nil} in the buffer.  This
is because unibyte buffers contain raw bytes, not characters, and thus
lack the directionality properties required for reordering.
Therefore, to test whether text in a buffer will be reordered for
display, it is not enough to test the value of
@code{bidi-display-reordering} alone.  The correct test is this:

@example
 (if (and enable-multibyte-characters
          bidi-display-reordering)
     ;; Buffer is being reordered for display
   )
@end example

  However, unibyte display and overlay strings @emph{are} reordered if
their parent buffer is reordered.  This is because plain-@sc{ascii}
strings are stored by Emacs as unibyte strings.  If a unibyte display
or overlay string includes non-@sc{ascii} characters, these characters
are assumed to have left-to-right direction.

@cindex display properties, and bidi reordering of text
  Text covered by @code{display} text properties, by overlays with
@code{display} properties whose value is a string, and by any other
properties that replace buffer text, is treated as a single unit when
it is reordered for display.  That is, the entire chunk of text
covered by these properties is reordered together.  Moreover, the
bidirectional properties of the characters in such a chunk of text are
ignored, and Emacs reorders them as if they were replaced with a
single character @code{U+FFFC}, known as the @dfn{Object Replacement
Character}.  This means that placing a display property over a portion
of text may change the way that the surrounding text is reordered for
display.  To prevent this unexpected effect, always place such
properties on text whose directionality is identical with text that
surrounds it.

@cindex base direction of a paragraph
  Each paragraph of bidirectional text has a @dfn{base direction},
either right-to-left or left-to-right.  Left-to-right paragraphs are
displayed beginning at the left margin of the window, and are
truncated or continued when the text reaches the right margin.
Right-to-left paragraphs are displayed beginning at the right margin,
and are continued or truncated at the left margin.

  By default, Emacs determines the base direction of each paragraph by
looking at the text at its beginning.  The precise method of
determining the base direction is specified by the @acronym{UBA}; in a
nutshell, the first character in a paragraph that has an explicit
directionality determines the base direction of the paragraph.
However, sometimes a buffer may need to force a certain base direction
for its paragraphs.  For example, buffers containing program source
code should force all paragraphs to be displayed left-to-right.  You
can use following variable to do this:

@defvar bidi-paragraph-direction
If the value of this buffer-local variable is the symbol
@code{right-to-left} or @code{left-to-right}, all paragraphs in the
buffer are assumed to have that specified direction.  Any other value
is equivalent to @code{nil} (the default), which means to determine
the base direction of each paragraph from its contents.

@cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
Modes for program source code should set this to @code{left-to-right}.
Prog mode does this by default, so modes derived from Prog mode do not
need to set this explicitly (@pxref{Basic Major Modes}).
@end defvar

@defun current-bidi-paragraph-direction &optional buffer
This function returns the paragraph direction at point in the named
@var{buffer}.  The returned value is a symbol, either
@code{left-to-right} or @code{right-to-left}.  If @var{buffer} is
omitted or @code{nil}, it defaults to the current buffer.  If the
buffer-local value of the variable @code{bidi-paragraph-direction} is
non-@code{nil}, the returned value will be identical to that value;
otherwise, the returned value reflects the paragraph direction
determined dynamically by Emacs.  For buffers whose value of
@code{bidi-display-reordering} is @code{nil} as well as unibyte
buffers, this function always returns @code{left-to-right}.
@end defun

@cindex visual-order cursor motion
  Sometimes there's a need to move point in strict visual order,
either to the left or to the right of its current screen position.
Emacs provides a primitive to do that.

@defun move-point-visually direction
This function moves point of the currently selected window to the
buffer position that appears immediately to the right or to the left
of point on the screen.  If @var{direction} is positive, point will
move one screen position to the right, otherwise it will move one
screen position to the left.  Note that, depending on the surrounding
bidirectional context, this could potentially move point many buffer
positions away.  If invoked at the end of a screen line, the function
moves point to the rightmost or leftmost screen position of the next
or previous screen line, as appropriate for the value of
@var{direction}.

The function returns the new buffer position as its value.
@end defun

@cindex layout on display, and bidirectional text
@cindex jumbled display of bidirectional text
@cindex concatenating bidirectional strings
  Bidirectional reordering can have surprising and unpleasant effects
when two strings with bidirectional content are juxtaposed in a
buffer, or otherwise programmatically concatenated into a string of
text.  A typical problematic case is when a buffer consists of
sequences of text ``fields'' separated by whitespace or punctuation
characters, like Buffer Menu mode or Rmail Summary Mode.  Because the
punctuation characters used as separators have @dfn{weak
directionality}, they take on the directionality of surrounding text.
As result, a numeric field that follows a field with bidirectional
content can be displayed @emph{to the left} of the preceding field,
messing up the expected layout.  There are several ways to avoid this
problem:

@itemize @minus
@item
Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
@acronym{LRM}, to the end of each field that may have bidirectional
content, or prepend it to the beginning of the following field.  The
function @code{bidi-string-mark-left-to-right}, described below, comes
in handy for this purpose.  (In a right-to-left paragraph, use
@code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.)  This
is one of the solutions recommended by the UBA.

@item
Include the tab character in the field separator.  The tab character
plays the role of @dfn{segment separator} in bidirectional reordering,
causing the text on either side to be reordered separately.

@cindex @code{space} display spec, and bidirectional text
@item
Separate fields with a @code{display} property or overlay with a
property value of the form @code{(space . PROPS)} (@pxref{Specified
Space}).  Emacs treats this display specification as a @dfn{paragraph
separator}, and reorders the text on either side separately.
@end itemize

@defun bidi-string-mark-left-to-right string
This function returns its argument @var{string}, possibly modified,
such that the result can be safely concatenated with another string,
or juxtaposed with another string in a buffer, without disrupting the
relative layout of this string and the next one on display.  If the
string returned by this function is displayed as part of a
left-to-right paragraph, it will always appear on display to the left
of the text that follows it.  The function works by examining the
characters of its argument, and if any of those characters could cause
reordering on display, the function appends the @acronym{LRM}
character to the string.  The appended @acronym{LRM} character is made
invisible by giving it an @code{invisible} text property of @code{t}
(@pxref{Invisible Text}).
@end defun

  The reordering algorithm uses the bidirectional properties of the
characters stored as their @code{bidi-class} property
(@pxref{Character Properties}).  Lisp programs can change these
properties by calling the @code{put-char-code-property} function.
However, doing this requires a thorough understanding of the
@acronym{UBA}, and is therefore not recommended.  Any changes to the
bidirectional properties of a character have global effect: they
affect all Emacs frames and windows.

  Similarly, the @code{mirroring} property is used to display the
appropriate mirrored character in the reordered text.  Lisp programs
can affect the mirrored display by changing this property.  Again, any
such changes affect all of Emacs display.

@cindex overriding bidirectional properties
@cindex directional overrides
@cindex LRO
@cindex RLO
  The bidirectional properties of characters can be overridden by
inserting into the text special directional control characters,
LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
(@acronym{RLO}).  Any characters between a @acronym{RLO} and the
following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
control character, whichever comes first, will be displayed as if they
were strong right-to-left characters, i.e.@: they will be reversed on
display.  Similarly, any characters between @acronym{LRO} and
@acronym{PDF} or newline will display as if they were strong
left-to-right, and will @emph{not} be reversed even if they are strong
right-to-left characters.

@cindex phishing using directional overrides
@cindex malicious use of directional overrides
  These overrides are useful when you want to make some text
unaffected by the reordering algorithm, and instead directly control
the display order.  But they can also be used for malicious purposes,
known as @dfn{phishing}.  Specifically, a URL on a Web page or a link
in an email message can be manipulated to make its visual appearance
unrecognizable, or similar to some popular benign location, while the
real location, interpreted by a browser in the logical order, is very
different.

  Emacs provides a primitive that applications can use to detect
instances of text whose bidirectional properties were overridden so as
to make a left-to-right character display as if it were a
right-to-left character, or vise versa.

@defun bidi-find-overridden-directionality from to &optional object
This function looks at the text of the specified @var{object} between
positions @var{from} (inclusive) and @var{to} (exclusive), and returns
the first position where it finds a strong left-to-right character
whose directional properties were forced to display the character as
right-to-left, or for a strong right-to-left character that was forced
to display as left-to-right.  If it finds no such characters in the
specified region of text, it returns @code{nil}.

The optional argument @var{object} specifies which text to search, and
defaults to the current buffer.  If @var{object} is non-@code{nil}, it
can be some other buffer, or it can be a string or a window.  If it is
a string, the function searches that string.  If it is a window, the
function searches the buffer displayed in that window.  If a buffer
whose text you want to examine is displayed in some window, we
recommend to specify it by that window, rather than pass the buffer to
the function.  This is because telling the function about the window
allows it to correctly account for window-specific overlays, which
might change the result of the function if some text in the buffer is
covered by overlays.
@end defun

@cindex copying bidirectional text, preserve visual order
@cindex visual order, preserve when copying bidirectional text
  When text that includes mixed right-to-left and left-to-right
characters and bidirectional controls is copied into a different
location, it can change its visual appearance, and also can affect the
visual appearance of the surrounding text at destination.  This is
because reordering of bidirectional text specified by the
@acronym{UBA} has non-trivial context-dependent effects both on the
copied text and on the text at copy destination that will surround it.

  Sometimes, a Lisp program may need to preserve the exact visual
appearance of the copied text at destination, and of the text that
surrounds the copy.  Lisp programs can use the following function to
achieve that effect.

@defun buffer-substring-with-bidi-context start end &optional no-properties
This function works similar to @code{buffer-substring} (@pxref{Buffer
Contents}), but it prepends and appends to the copied text bidi
directional control characters necessary to preserve the visual
appearance of the text when it is inserted at another place.  Optional
argument @var{no-properties}, if non-@code{nil}, means remove the text
properties from the copy of the text.
@end defun