Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/not-wf/P69/ibm69n02.xml
<!DOCTYPE root [ <!ELEMENT root (#PCDATA)> <!ENTITY % paaa "<!ATTLIST root att CDATA #IMPLIED>"> <!--* incorrect PE reference without semicolon *--> %paaa <!ENTITY aaa "aString"> ]> <root/>