diff --git a/mmeval/metrics/char_recall_precision.py b/mmeval/metrics/char_recall_precision.py
index c798e702..aaebf230 100644
--- a/mmeval/metrics/char_recall_precision.py
+++ b/mmeval/metrics/char_recall_precision.py
@@ -7,15 +7,17 @@
 
 
 class CharRecallPrecision(BaseMetric):
-    """Calculate the char level recall & precision.
+    r"""Calculate the char level recall & precision.
 
     Args:
         letter_case (str): There are three options to alter the letter cases
+
             - unchanged: Do not change prediction texts and labels.
             - upper: Convert prediction texts and labels into uppercase
                      characters.
             - lower: Convert prediction texts and labels into lowercase
                      characters.
+
             Usually, it only works for English characters. Defaults to
             'unchanged'.
         valid_symbol (str): A regular expression to filter out invalid or