Re: predicate group-p to see if a group exists?

[Richard Stallman <rms@gnu.org>]

    Granted, most users of `defgroup', `defcustom', and `defface' will not need
    to test whether a given group exists, but some will. I still have the
    question whether we shouldn't have a function `group-p'.

Until we see a more than a handful of cases where testing 
the existence of a custom group is the right thing to do,
let's not spend any time on this.

Every function added to Emacs has a real cost, which includes writing
it, maintaining it, documenting it, etc.  It requires a justification
stronger than "maybe someone will find it useful".  In this case,
justification is not present.