Some Non-Interoperable Declarations

This sentence perhaps tries to pack too much into too little space. Suppose you have a declaration as follows:

<!ATTLIST e a1 CDATA #IMPLIED>

Then, none of the following would meet the conditions here for interoperability:

<!-- 2nd attribute-list declaration for element type "e" -->
<!ATTLIST e a2 CDATA #IMPLIED>
<!-- 2nd declaration for attribute "a2" -->
<!ATTLIST e a2 IDREF #REQUIRED>
<!-- empty attribute-list declaration -->
<!ATTLIST e >

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