SR=0 wrt MAXREC=0 text clarification

[molinaro-m]

In the porting of the REC-1.03 to the current document SR=0 was described as identical with MAXREC=0.
Since this is not exactly true the analogy among these two parameters has to be relaxed.
(anyway the actual goal is the same, thus MAXREC=0 is encouraged w.r.t. SR=0)

[molinaro-m]

Re-opening the issue because of the revision 1.1 refactoring.
Can be closed once #57 gets in place.

[molinaro-m]

closed via PR #57

[msdemlei]

Actually, there's a rabbit hole here. I'd like to argue that 1.03 has made no requirement that SR=0 actually returns no records.

And there is a point why one might want to do that: a catalogue of extended objects. I have a few of those, and two that even overlap the coordinate system origin: ivo://org.gavo.dc/cstl/q/cone and ivo://org.gavo.dc/amanda/q/cone. These are currently caught by a validator that insists on SR=0 returning no records.

The way these services are implemented, they return whenever the objects overlap the search region. If the search region is a point, that's a simple area-contains-point test. Since the implementation is straightforward and it seems to me the expectable behaviour... Well, can we explicitly state that it's ok to return records for SR=0?

If not, then we'll have to make the prohibition explicit. That that requires extra code in my case, I'd at least request a good use case that induces that requirement...