OPTGROUP is a grouping element that can be used in SELECT elements. For instance instead of...
Which Web browser do you use most often?
...you might see...
Which Web browser do you use most often?
(That sample courtesy of the OPTGROUP page above, which is why the browser list is obsolete. I'm too lazy to update it)
Whether you see those or not depends on your browser (some ancient ones dislike form elements that aren't in a form), and the visual styling of the group headers will differ.
It's a pretty useful little addition to HTML, and has been around for quite some time. Remarkable, then, that it has seen negligible use in the real world. This despite the fact that it is eminently useful, clear by the fact that lots of sites are doing exactly this sort of thing manually: Adding custom hacked in groupings, where the group headers themselves are selectable but not really selectable (it'll be script-overridden or refused by the form handler if it is selected by the user, which is confusing from a UI perspective) for things like grouping states and provinces by country, and so on.
Of course my point here wasn't to evangelize OPTGROUP, though I do think that it's underused. The profound thing to me, brought to mind by the power of this trivial and underused element, is how marginal the advances in web technology (specifically HTML) have been over the past several years. Everyone is busy doing grossly redundant scripting and hackery for the most mundane of things, trying to use the coarse paintbrush available to build a subpar pseudo-fat client. Maybe they're spending weeks trying to replace their table layout with DIVs to satisfy the XHTML pedants.
How many lame derivatives of combo-boxes have been hacked out? How many intolerable scripted spell checkers? How many hacked out date/time selectors? Every one of them a mystery-meat to unwilling web victims.
Doesn't it seem reasonable that these things could be a part of the basic toolset of HTML by now, allowing rich clients to use their power to present it in the most intelligent way possible?
For that matter, why haven't we made the leap to "databound" controls? Would it really be that difficult to standardize some of the standard "AJAX" type functionality into declarative HTML 5.0? Not only is AJAX far from new, but the fundamentals behind it have been understood since the nascent days of the web. This is painfully obvious stuff.
Is it really that difficult?
Of course, it absolutely would be that difficult. Once a standard is entrenched, it becomes more and more difficult to change through consensus.
History is rife with examples where someone hacked something together and unleashed it on the world, and it was good, and it was revolutionary. The rate of innovation quickly slows, though, as more and more people get involved, and their vested interests and aversion to change takes hold, to the point that the most ridiculously trivial and profoundly necessary of changes take years to see the light of day. RSS feeds are just barely gaining traction, yet already many evangelists have their feet firmly stuck in the concrete, unwilling to even consider trivial changes. For instance alternatives to the absurd RSS/XML icon (who knew that people could get so defensive over a 36x14 icon). RSS will eventually rust, until some new disruptive standard comes along and eats its lunch, and then it will repeat. It is the way these things tend to go.
Oh well, I hear that they're developing Duke Nukem Forever using XForms.
