group by expression - syntax?

[Mark Lanzo]

On 14 Jul, Helmut Jarausch wrote:
> Hi,
> 
> can anybody tell me about the syntax of an expression for
> 'group by expression'?
> It doesn't seem to be a usual regular expression, e.g.
> I wanted to group all mails having  '[scons-users]'
> in their subject field.
> But I didn't manage to get such a selection.
> I tried  '\[scons-users\]' but surprisingly that
> selected all mails.

Yeah, I noticed the same problem.  Seems that the strings
that are entered for regexp are ccidentally scanned
TWICE for metachars, at least for "\".  I think perhaps
"\[scons-users\]" is getting turned into "[scons-users]" 
before even calling the regexp matcher, with the consequence
that the regexp matches anything containing the letters
c,e,n,o,r,s,t,u.  Oops!

As a workaround, try "\\[scons-users\\]"