<?xml version="1.0"?>
<!DOCTYPE doc [
<!ATTLIST elem xmlns CDATA #FIXED "urn:def2">
<!ATTLIST elem xmlns:a CDATA #FIXED "urn:a2">
]>
<doc xmlns="urn:def" xmlns:a="urn:a">
    <elem xmlns="urn:def2" xmlns:a="urn:a2"/>
</doc>