[CSS21] [css3-selectors] case-sensitivity of :lang()

Currently :lang() is defined as doing |= match against the
language string (normalized to RFC 3066 format per [1]).

It's not clear whether this match is case-sensitive or
case-insensitive. Since language codes are case-insensitive,
I believe this match should be case-insensitive. I've tested
Opera, Safari, and Firefox, and they agree.

Proposed that in
   http://www.w3.org/TR/CSS21/selector.html#lang
and
   http://www.w3.org/TR/css3-selectors/#lang-pseudo
the phrase
   "in the same way as if performed by the '|=' operator."
be replaced by
   "in the same way as if performed by the '|=' operator
    except that in this case a case-insensitive match is
    performed."


On a related note, while Opera and Firefox treat |= as
performing a case-sensitive match (which, afaict from
the spec, it should), Safari treats it as case-insensitive.

~fantasai