http://java-sl.com/custom_tag_html_kit.html is no longer available.

That previous link only provided a workaround, but in fact you can easily and properly extend support for Swing HTML tags. You can also get HTML5 support if you want, but it would be a lot of work and the performance would be far from that of a real web browser.

Javax Swing HTML parser is a DTD driven parser. The default DTD is called html32.dtd, meaning it supports most of HTML 32 recommendations.

If you want to support more Tags, you have to extend or rewrite this DTD. For example, below, MathML support was added to Swing HTML :

A bug report was submitted to make this easier : Add Reference or Informations About DTDBuilder in Documentation

Beware :

• This is the first step to support your tag. Next, you had to design its rendering and register it in the View factory.
• Swing Text HTML is not for read HTML documents from the World Wide Web.
• Modern WebBrowsers don't use DTD approach.
• DTD approach makes sens if you want to have a strict control of your document structure in a project with the ability to export to World Wide Web but without the need to read real World HTML Documents. The DTD may stuck with malformed documents.
• Think of Swing HTML as a Wordpad where underlying document structure is HTML.

This responce was extracted from Which HTML tags are supported in Swing components ?.