result/valid/ns2.xml

<?xml version="1.0"?>
<!DOCTYPE a:outer [
<!ELEMENT a:outer (a:inner)>
<!ATTLIST a:outer xmlns:a CDATA #FIXED "urn:namespace">
<!ELEMENT a:inner EMPTY>
<!ATTLIST a:inner xmlns:a CDATA #FIXED "urn:namespace">
<!ATTLIST a:inner attr CDATA #FIXED "yes">
]>
<a:outer xmlns:a="urn:namespace">
  <a:inner xmlns:a="urn:namespace"/>
</a:outer>