Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/not-wf/P77/ibm77n04.xml
<!DOCTYPE root [ <!ELEMENT root (#PCDATA)> <!ATTLIST root att CDATA #IMPLIED> <!--* error in external entity *--> <!ENTITY % pExternal SYSTEM "ibm77n04.ent"> %pExternal; ]> <root/>