Joss, the list of suggested MUSTs etc is useful although some of these
> I don't know where it is specified that the request may be
> echoed in SRU
> but it should better be a must too. The server is allowed to ignored
> additional request extensions it does not understand - so it should
> return the query that was actually executed.
I've always wanted this to be a must - however some have argued that
this should only be a should.