All the files must contain the CVS Id header. If you create a new file, the first line must be:

<!-- $Id: -->

The first time it is committed to CVS (and every time it is committed to CVS) the line is updated automatically to include information about the file. For example:

<!-- $Id: sn-xml-guidelines-header.php,v 1.3 2007/09/16 19:16:25 pfrields Exp $ -->