Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/not-wf/P89/ibm89n07.xml
<!DOCTYPE animal [ <!ELEMENT animal ANY> <?_〆 an illegal extender #x3006 in PITarget ?> ]> <animal/> <IllegalExtender〆/>