A comma separated list of collection ids to search against. Leaving this blank means it will search across
all identifiers. Entity defs can be constrained to specific facets by providing them as facet collections.
Relationship collections will resolve to their underlying entity def.
Collection ids are: organizations, people, funding_rounds, acquisitions, investments, events,
press_references, funds, event_appearances, ipos, ownerships, categories, category_groups, locations, jobs
