I think the ID part should be fixed in CVS now and will be in the
next release:

orchis:~/XML -> cat test/XInclude/docs/docids.xml 
<!DOCTYPE book [
<!ELEMENT book (doc*)>
<!ELEMENT doc (isid*)>
<!ELEMENT isid EMPTY>
<!ATTLIST isid myid ID #IMPLIED>
]>
<book>
<doc>
<isid myid="mine"/>
<isid myid="dup"/>
</doc>
<!-- including another XML document with IDs -->
<xinclude:include xmlns:xinclude="http://www.w3.org/2001/XInclude"
		 href="../ents/ids.xml"/>
</book>
orchis:~/XML -> cat test/XInclude/ents/ids.xml    
<!DOCTYPE doc [
<!ELEMENT doc (isid*)>
<!ELEMENT isid EMPTY>
<!ATTLIST isid myid ID #IMPLIED>
]>
<doc>
<isid myid="dup"/>
<isid myid="foo"/>
<isid myid="bar"/>
</doc>
orchis:~/XML -> xmllint --xinclude --shell test/XInclude/docs/docids.xml
/ > dir id('foo')
ELEMENT isid
  ATTRIBUTE myid
    TEXT
      content=foo
/ > 

  The IDs from the included Infoset have been merged in the
resulting infoset, and then available to XPath,

  This should fix your problem :-)

Daniel

The libxml2-2.4.15 / libxslt-1.0.12 release should fix the problem,

  thanks,

Daniel