Profile resolver spec: Notation in metadata section

[galtm]

I'm having trouble understanding some notation in the Metadata Resolution section of the Profile Resolution spec. The notation metadata:last-modified describes what in XML becomes a child element named last-modified. This child element is listed in the catalog model. However, similar notations metadata:source-profile and metadata:resolution-tool map in XML to markup forms in a sample document that are not elements named source-profile or resolution-tool:

      <prop name="resolution-tool" value="some value"/>
      <link rel="source-profile" href="../base-test_profile.xml"/>

What does the colon mean in the spec syntax, and is there a legend for it?