Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/sun/not-wf/attlist02.xml
<!DOCTYPE root [ <!ELEMENT root EMPTY> <!-- SGML-ism: illegal attribute types --> <!ATTLIST root number NUTOKENS "1 2 3" > ]> <root/>