Underscore problem

Greetings,
  I will begin this mail by making showing you my understanding in this
matter - I am aware of the CSS standards and appreciate the versatility
of CSS in every page I have ever made :)
However, I was somewhat sad to find out that the common underscore ("_")
was non-valid in classnames in CSS. My first reaction was "What? Must be
something in my sheet.." but I searched just to find that my stylesheet
was quite accurate, except from the underscore. So my next question was
"Why?". So I now ask you: Why do you not allow underscores to be a part of
classnames? The Mozilla parser accept underscores in classnames, so does
the parser used by Internet Explorer (I have not checked the exact version
in which they function). I have chosen to ignore the rule about
underscores because of the very common use of underscores in good
variable-naming and in this case: class-naming. I heard something about
that the character "dash" ("-") is valid but I'd really like to use
underscore, since a dash has a more "grouping" sense, e.g.: you would use
dashes in word-combining, but underscores in grouping (e.g.: main_menu,
main_content, etc.) - I hope you get the point.. I don't expect to flip
the css standards upside-down, but I hope that my mail will, in best case
scenario, change that small fact that underscores, such a well-used
character, will be valid CSS in future CSS version.

- Seph Soliman,
Lead developer, clanhost.dk