HtmlUnit is a "browser for Java programs". It models HTML documents and provides an API that allows you to invoke pages, fill out forms, click links, etc... just like you do in your "normal" browser.
In SVN version, HtmlUnit has recently added all HTML elements (some are rarely used), which may have some backward compatibility effect in the next version 2.5
For example, <b> was evaluated to HtmlUnknownElement, but now will be HtmlBold.
The complete list includes: HtmlAbbreviated, HtmlAcronym, HtmlBackgroundSound, HtmlBig, HtmlBlink, HtmlBold, HtmlCitation, HtmlCode, HtmlDefinition, HtmlEmphasis, HtmlExample, HtmlItalic, HtmlKeyboard, HtmlListing, HtmlMarquee, HtmlMultiColumn, HtmlNoBreak, HtmlNoEmbed, HtmlPlainText, HtmlS, HtmlSample, HtmlSmall, HtmlSpacer, HtmlStrike, HtmlStrong, HtmlSubscript, HtmlSuperscript, HtmlTeletype, HtmlUnderlined and HtmlVariable.
Feel free to get latest snapshot from http://build.canoo.com/htmlunit/artifacts
Enjoy testing!