Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/invalid/P69/ibm69i02.dtd
<!ELEMENT a EMPTY> <!ENTITY ge1 "abcdef"> <!ATTLIST a attr1 CDATA "&ge1;"> %pe1; <!--* PE reference in attr default before declaration *--> <!ENTITY % pe1 "<!ATTLIST a attr2 CDATA #IMPLIED>">