A bogon is an element that appears in an HTML document, but has never been recognized by any browser. You’ll often find them by viewing source on pages written by XML geeks like me. I got the term from John Cowan’s TagSoup, which has, a
--nobogons switch to suppress any elements it doesn’t recognize.
A semibogon (my own coinage) is an old element that used to be recognized by one or more browsers but is no longer. Examples include:
I’m trying to generate a reasonably complete list of these semibogons for Refactoring HTML. Can anyone add to this list?