All GNOME documentation should conform to XML syntax requirements, which are stricter than SGML ones -- see the section called “XML and SGML” for more informaion.
Application documentation should identify the version of the application for which the documentation is written:
<sect1 id="intro"> <title>Introduction</title> <para> blah-blah-blah This document describes version 1.0.53 of gfoo. </para> </sect1>
Application documentation should contain a copyright notice, stating the licensing terms. It is suggested that you use the GNU Free Documentation License. You could also use some other license allowing free redistribution, such as GPL or Open Content license. If documentation uses some trademarks (such as UNIX, Linux, Windows, etc.), proper legal junk should also be included (see templates).