Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/not-wf/P64/ibm64n03.dtd
<?xml version="1.0" encoding='UTF-8'?> <!--dtd for production 64--> <![IGNORE[ start <!ELEMENT animal EMPTY> ]]> end ]]> <!--Negative test. Missing opening sequence-->