Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/xmltest/valid/sa/059.xml
<!DOCTYPE doc [ <!ELEMENT doc (e*)> <!ELEMENT e EMPTY> <!ATTLIST e a1 CDATA #IMPLIED a2 CDATA #IMPLIED a3 CDATA #IMPLIED> ]> <doc> <e a1="v1" a2="v2" a3="v3"/> <e a1="w1" a2="v2"/> <e a1="v1" a2="w2" a3="v3"/> </doc>