Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/valid/P68/ibm68v01.xml
<?xml version="1.0"?> <!DOCTYPE root SYSTEM "ibm68v01.dtd" [ <!ELEMENT root (#PCDATA|a)* > ]> <root> pcdata content <a attr1="xyz"/> </root> <!--* a valid test for P68 VC:Entity Declared *-->