Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/invalid/P49/ibm49i01.dtd
<!ELEMENT a EMPTY> <!ELEMENT b (#PCDATA|c)* > <!ELEMENT c ANY> <!--* open and close parenthesis are in different PE replace Texts *--> <!ENTITY % choice1 "(a|b"> <!ENTITY % choice2 "|c)"> <!ELEMENT child1 %choice1;%choice2; >