There are two different situations where xml is parsed.

One situation is the Cocoon/Forrest processing of xml contnet.

The other situation is the 'forrest validate-xdocs' target.
This latter is an Ant target. See $FORREST_HOME/main/targets/validate.xml
This uses the Ant task "xmlvalidate". This can set "features"
of the parser.
See http://ant.apache.org/manual/OptionalTasks/xmlvalidate.html

If you can find a feature about expanding included xml before
validating, then we can can declare that feature.
http://xerces.apache.org/xerces2-j/features.html

-David