bug#7217: 24.0.50; no doc strings for regexp-opt functions

[Drew Adams]

> > Please provide doc strings for the so-called "workhorse" regexp-opt
> > functions.  They are important enough for users that I see 
> > them used in 3rd-party libraries.
>  
> >  regexp-opt-group
> >  regexp-opt-charset
> 
> Maybe regexp-opt-charset makes sense in 3rd party libraries (the same
> functionality is also re-implemented in rx.el and sregex.el, 
> IIRC), but I can't think of any reason to use regexp-opt-group.
> 
> So I agree for regexp-opt-charset and would also like to see 
> it used in rx.el and friends,

Sounds good to me.  r-o-c was in fact the one I came across in a 3rd-party
library - I should have said "it", not "them".

(However, I cannot see any reason _not_ to give doc strings to both.  I
understand that you feel that way about "internal" functions.  I don't.  Doc
strings make it easier to read code.  If a block comment at the beginning of a
function to describe it is useful for reading the code, then turn it into a doc
string so it becomes easier to access.  In the 1980s there was also a desire to
save some space/memory, but that should no longer be a consideration wrt doc
strings.)