I love how people try to get file extensions into three letters these days, but really, why bother? Semantic value is everything - the extension .html tells you that the file contains something that someone, someone believes can be vaguely shoehorned into the category of "HTML code"; .lasso tells you it might be a Lasso file, .pl for Perl or Prolog. I can't think of any reason not to use .html - apart from of course these cases!
- You haven't had your morning coffee yet.
- You're using PC/MS/MR/4/whatever - DOS, which only supports 8.3 format filenames. Your webserving software also uses this. You probably use token ring cards in your network, which took four painstaking weeks to set up with TCP/IP. There are no known webservers for your OS, so you wrote one in Turbo Pascal.
- You don't think there are enough TLAs in the world, and would like to create more. No, that doesn't mean Text Link Ads.
- You code a special way, using HyperText Markup. It's not a Language (seriouly, the way you're going at it, it really isn't).
- Your 'L' key doesn't work (not really an excuse).
- The idiot who set up / mangled your webserver config doesn't believe in HTML, or leaving home, or having anyone but his mother do his laundry.
Seriously, there's no need to bother with three letter extensions. You're not using DOS / Novell / whatever, your clients aren't, your webserver (if it's a good one running on a proper OS) has never even recognised extensions and so definitely doesn't care about their lengths. If you're stuck to them, there's a spanner in your works.