I was working with a file that I needed to have sed match a group
of characters with square brackets in.  Is there a way to do that?
I can't find my copy of the POSIX spec at the moment, but while
that might help figure out all the legal ways to put the RE together,
it doesn't always help much with a "How do I..." question.

Neither [#[]@ ] nor [#\[\]@ ] worked, in fact, just adding the
brackets made the group not match anything at all. (Or caused an
error, depending on the exact way I tried to put it together.)

Jon