expressing limits on result set

All practical search systems impose limits on the size of result sets
and/or the amount of computational effort to be expended in creating them.
Queries that exceed these limits either fail or return a truncated result set.

If the protocol does not already do so (I can't check right now) it should
include explicit means of signalling when such limits are exceeded, and it
should include means for clients to request (presumably smaller) limits in
seaches.