http://hl7.org/fhir/StructureDefinition/cqf-isSelective|5.2.0

Allows a given data requirement to be identified as \"selective\", meaning that it can be used as an additive criteria to filter a population. A selective data requirement is guaranteed to define a subset (not necessarily proper) of the initial population of an artifact. If multiple data requirements are marked selective, they all apply (i.e. AND semantics).