Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/invalid/P50/ibm50i01.dtd
<!ELEMENT a EMPTY> <!ELEMENT b (#PCDATA|c)* > <!ELEMENT c ANY> <!--* PE replace Text has no closing parentheses *--> <!ENTITY % choice1 "(a,b,c"> <!ELEMENT child1 (%choice1;)|c) >