Many of us write HTML documents with math and other
fancy symbols in them.
We want this to look nice on "all" browsers (or
at least as many browsers as possible) which is
not entirely trivial. There are a lot of tricks
that work OK on one platform but are not portable.
There are various pieces to this puzzle, including
-- eight-bit character encodings
-- unicode
-- HTML entity encodings of various types
-- Symbol-font kludges
-- et cetera
Some of this was not at all easy to figure out,
although the end-point makes a certain amount of
sense. For the sort of things people on this list
do, I basically recommend using decimal HTML entity
codes for anything that's not 7-bit ascii ... plus
a couple of kludgey exceptions to provide MSIE
compatibility.