Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/not-wf/P63/ibm63n02.xml
<?xml version="1.0"?> <!-- syntax test for Production 63--> <!DOCTYPE animal SYSTEM "ibm63n02.dtd" [ <!ATTLIST attr a (tiger) #REQUIRED> ]> <animal a = "TIGER1"> Negative test. Extra '[' is used before IGNORE. </animal>