A DESCRIPTION OF THE PROBLEM :
Javax Swing Html Parser is a driven DTD-HTML parser.

The aim of JDK-6190716 was to opensourced DTDBuilder.
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=6190716

This Done now but some Developers, including me, still was stuck when they wanted to alter the default DTD used with HTML classes, only because we ignored that such tool exists.

I suggest to add a reference or informations about DTDBuilder tool in the Java Documentation. For example, in the HTML Package Summary : https://docs.oracle.com/en/java/javase/18/docs/api/java.desktop/javax/swing/text/html/parser/package-summary.html

I can write such comments if you're interested.
I used DTDBuilder to produce an HTML+MathML DTD :
https://github.com/w3c/mathml-core/issues/51#issuecomment-823045966

This report follows a PR, I already send about a DTDBuilder's bug prevented its usage as indivudal tool :
https://github.com/openjdk/jdk/pull/3626