Created attachment 277133 [details]
testcase (see ReadMe file)

Relax NG is broken: I get an Relax NG parser error on correct .rng files.
See attached testcase.

$ xmllint --relaxng test1.rng test.xml
test1.rng:3: element include: Relax-NG parser error : xmlRelaxNG: include docbook.rng has a define subscript but not the included grammar
dbpoolx.rng:10078: element define: Relax-NG parser error : Some defines for subscript needs the combine attribute
Relax-NG schema test1.rng failed to compile
<?xml version="1.0"?>
<para>test</para>

But if I replaced the <include href="dbpoolx.rng"/> in docbook.rng by the file (with the needed changes such as removing the grammar element), the error disappears:

$ xmllint --relaxng test2.rng test.xml
<?xml version="1.0"?>
<para>test</para>
test.xml validates

This issue is similar to:

  https://mail.gnome.org/archives/xml/2003-March/msg00037.html

but the testcase on this page works fine with the current libxml2 version.

Test under Debian/unstable with the libxml2 2.9.1+dfsg1-3 package.