See test test/langtools/jdk/javadoc/doclet/testHtmlVersion/TestHtmlVersion.java

When run with JavadocTester.checkLinks, some broken links are revealed, caused by references to the enum's constructors. But the constructors for an enum are not documented and there should be no reference to them in any generated file.

out-3/index-all.html:264: id not found: out-3/pkg/AnotherClass.ModalExclusionType.html#ModalExclusionType--
out-3/index-all.html:426: id not found: out-3/pkg2/TestEnum.html#TestEnum--
out-2/index-all.html:264: id not found: out-2/pkg/AnotherClass.ModalExclusionType.html#ModalExclusionType--
out-2/index-all.html:426: id not found: out-2/pkg2/TestEnum.html#TestEnum--
out-1/index-all.html:269: id not found: out-1/pkg/AnotherClass.ModalExclusionType.html#<init>()
out-1/index-all.html:431: id not found: out-1/pkg2/TestEnum.html#<init>()