This is the ValueSet that contains all the codes in CDAActClassObservation (http://hl7.org/cda/stds/core/ValueSet/CDAActClassObservation) and CDAActClassObservation (http://hl7.org/cda/stds/core/ValueSet/CDAActClassObservation). E.g. what you have to deal with if you get resources containing codes in either of them