Addressing Lease/Embargo (and other) Visibility constraints in Samvera

proposal.txt

SAMVERA PROPOSAL:
"Scope of visibility" questions should resolve to (multivalued) date range fields:
  ~ visibility_public_drsim
  ~ visibility_institution_drsim
  ~ etc.

For each non-private vis. type the user has access to, queries of the form, e.g.: 
  "-visibility_public_drsim:[* TO *] OR visibility_public_drsim:NOW"

That is to say: "either it doesn't have visibility_public date period, or that period intersects now"

Advantages: 
~ solves the complete problem.
~ combines both lease and embargo elements, allows multiples of each if desired 
~ allows calendar visualization from indexed doc, both user and admin views