<its:rules xmlns:its="http://www.w3.org/2005/11/its" xmlns:dbk="http://docbook.org/ns/docbook" version="2.0">
  <its:externalResourceRefRule selector="//dbk:imagedata | //dbk:audiodata |  //dbk:videodata" externalResourceRefPointer="@fileref"/>
 </its:rules>
