Comments are text added to the form that is ignored by XFDL processors. This allows form developers to document the form from within the XFDL source code. This helps subsequent form and application developers to immediately understand the purpose of a particular block of markup, such as a complex compute or function call. Comments are always wrapped in a special sequence of characters that indicate the beginning and end of a comment section.
XFDL respects the standard XML comment style, which opens with <! -- and closes with -->. For example:
<! -- This is a code comment. -->
Because XFDL is an XML vocabulary, comment blocks can be of any length, from one line to multiple lines.