The World Wide Web Consortium (W3C) have a working draft for HTML 3.2.
(As quoted from W3C's HTML 3.2 Reference Specification)
HTML 3.2 is W3C's specification for HTML, developed in early `96 together with vendors including IBM, Microsoft, Netscape Communications Corporation, Novell, SoftQuad, Spyglass, and Sun Microsystems. HTML 3.2 adds widely deployed features such as tables, applets and text flow around images, while providing full backwards compatibility with the existing standard HTML 2.0.
This page will allow you to test a browser's/navigator's compliance with the final draft of HTML 3.2 markup tags.
Well-designed Web client software will not "break" when it encounters an unknown tag, it will just ignore it.
For more information about the W3C, click here.