Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/xml-1.1/valid/P03/ibm03v07.xml
<?xml version="1.1"?> <!DOCTYPE doc [ <!ELEMENT doc (#PCDATA)> <!ENTITY e " "> <!ATTLIST doc a CDATA #IMPLIED> ]> <doc>x&e;y</doc>