Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/libraries/HaXml/tests/xml-conformance/xmltest/valid/sa/094.xml

<!DOCTYPE doc [
<!ENTITY % e "foo">
<!ELEMENT doc (#PCDATA)>
<!ATTLIST doc a1 CDATA "%e;">
]>
<doc></doc>