> I know that Rob has already addressed these points, but it really
> can't be said too many times.  SRW/U implementations simply may not do
> this.  They're just not allowed.  It's not an implementation-level
> decision, but a protocol-level one.

Hold on. There are good reasons  (in some situations) for a server not to
send unsolicited data, and good reasons (in some situations)  to do so, as
Rob and Bill respectively have pointed out.  I noted when this discussion
came up before that I would define an extension "permission to send
unsolicited  data" and everyone seemed comfortable with this approach.

To this end I have defined  this extension, listed at
http://www.loc.gov/z3950/agency/zing/srw/extra-data.html#infoURI

info:srw/extension/1/will-accept-any-extra-data

 So if a client is prepared to accept unsolicited extra data it includes
this extension in the request.  If it doesn't include it, then the rules
disallowing unrequested extra data prevail.
--Ray