Read it more carefully. It says that while the following are legal
in XML, they will be rejected by pre-TC SGML systems, so if you care
about such systems, you shouldn't use them:
<!ATTLIST e a1 CDATA #IMPLIED>
<!-- warning applies from here down -->
<!ATTLIST e a2 CDATA #IMPLIED> <!-- 2 attlists for type "e" -->
<!ATTLIST e a2 IDREF #REQUIRED> <!-- 2 defs for attr "a2" -->
<!ATTLIST e > <!-- empty attlist -->
Need another annotation here... -T.