Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/ibm/xml-1.1/not-wf/P77/ibm77n17.xml
<!DOCTYPE doc [ <!ELEMENT doc (root*)> <!ELEMENT root EMPTY> <!ENTITY e SYSTEM "ibm77n17.ent"> ]> <doc>&e;</doc>