Implementations of hook_islandora_doi_framework_check_for_doi should query the registrar's API

[mjordan]

It is probably a good idea to do a two-pass check to see if an object already has a DOI, once in the local persist location (e.g. MODS, DDI) and then in a public metadata registry like DataCite Search. The latter would probably need to assume that there is some unique data in the metadata, like a local identifier.

The API docs for this hook should be updated to explain this.