/usr/share/empathy/empathy-contact-groups.dtd is in empathy-common 3.4.2.3-2+deb7u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | <!--
DTD for Empathys contact groups.
by Martyn Russell <mr@gnome.org>
-->
<!-- Root element. -->
<!ELEMENT contacts (account)>
<!ELEMENT account (group)+>
<!ATTLIST account
name CDATA #REQUIRED>
<!-- Groups in the roster. -->
<!ELEMENT group EMPTY>
<!ATTLIST group
name CDATA #REQUIRED
expanded CDATA #REQUIRED>
|