group by expression - syntax?

[Helmut Jarausch]

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.

Many thanks for a hint,

Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany