<grammar xmlns="http://relaxng.org/ns/structure/1.0"> <define name="XLINK.xmlns.attrib"> <empty/> </define> <define name="Schema.xmlns.attrib"> <empty/> </define> <define name="MATHML.xmlns.extra.attrib"> <ref name="XLINK.xmlns.attrib"/> <ref name="Schema.xmlns.attrib"/> </define> <define name="MATHML.xmlns.attrib"> <ref name="MATHML.xmlns.extra.attrib"/> </define> </grammar>