<?xml  version="1.0"?>
<!-- validity constraint check for Production 56(Negative Test)-->
<!DOCTYPE test
 [
 <!ELEMENT test ANY>
 <!ELEMENT id EMPTY>
 <!ELEMENT idref EMPTY>
 <!ATTLIST id UniqueName ID #REQUIRED>
 <!ATTLIST idref reference IDREF #IMPLIED>
 ]>
<test>
<id UniqueName = "AC456"></id>
<idref reference = "@456"></idref>
Negative test for validity constraint of IDREF.
In an attribute decl, values of type IDREF does not match the name production
</test>