This is the set of resources that conform to either of the profiles Reaction Observation (http://hl7.org/cda/us/ccda/StructureDefinition/ReactionObservation) and Reaction Observation (http://hl7.org/cda/us/ccda/StructureDefinition/ReactionObservation). E.g. what you have to deal with if you get resources conforming to one of them