Documentation notation question

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxx>]

In the section "Parameters Set By The Shell", many parameter names have <S>,
<Z> or both tags.  The meaning of these tags isn't explained anywhere that I
can find.  I would have guessed it had something to do with starting zsh as
sh or ksh, except that some of the parameters don't have any notation at all,
and I can't figure out what that means (unless it means the same as both, in
which case why -ever- have both?).

So what are <S> and <Z> for?

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com