Bogons and Semibogons

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:

  • marquee
  • basefont
  • bgsound
  • keygen
  • bgsound
  • spacer
  • wbr
  • nobr

I’m trying to generate a reasonably complete list of these semibogons for Refactoring HTML. Can anyone add to this list?

10 Responses to “Bogons and Semibogons”

  1. Mark Says: has it all. APP, MULTICOL, HTMLPLUS… the list is longer (and weirder) than most people realize.

  2. David Håsäther Says:

    You can find some other obscure ones at

  3. Jim Says:


  4. Elliotte Rusty Harold Says:

    Layer is a good one to remember, though I think it does still have an effect in some browsers today. Who ever had a comment or image element?

  5. Jim Says:

    I seem to remember layer is special-cased in some way in KHTML. Apart from that, only Netscape 4 knows about it as far as I know.

    comment and image go back to Mosaic era, but I’m not sure exactly which browsers supported them.

  6. James Abley Says:

    bgsound – so good they used it twice!

  7. Mark Says:

    To answer the second half of your question (which elements are still supported in modern browsers), lists all elements recognized by Firefox. Search for “kExtensions” to pinpoint ones that aren’t part of any specification.

  8. Ian Hickson Says:

    marquee, basefont, bgsound, keygen, and wbr are all supported by most modern browsers.

  9. Philippe Lhoste Says:

    > marquee, basefont, bgsound, keygen, and wbr are all supported by most modern browsers.

    marquee, like blink, should be obsolete… So is bgsound (twice in the list above).
    basefont too, like font, CSS is here to bury them.
    keygen, I don’t know much about it.
    wbr, I discovered it here, and found it at which shows alternatives. An interesting tag.

  10. Brett Says:

    I’ve gathered all the ones I could find in this Tidy feature request: . This is a very helpful resource: