http://fhir.patientsknowbest.com/operation/group
https://www.hl7.org/fhir/STU3/operationdefinition.html
https://www.hl7.org/fhir/STU3/operations.html
name
"group"
status
"active"
...
An existing example of this is the$lastn operation.
More general grouping behaviour can be achieved by using the custom $group operation (for supported endpoints).
...