When passing resources as parameters, there's sometimes an expectation that there will be a relationship between some of the parameters. I.e. one of the resources is expected to point to another resource. Recommend adding the following to OperationDefinition.parameter:
references 0..* BackboneElement; short: "references to this parameter"; definition: "Identifies other resource parameters within the operation invocation that are expected to resolve to this resource"; comment: "Resolution applies if the referenced parameter exists."
references.source 1..1 string; short: "referencing parameter"; definition: "The name of the parameter or dot-separated path of parameter names pointing to the resource parameter that is expected to contain a reference to this resource"
references.sourceElement 0..1 string; "element id of reference"; definition: "The id of the element in the referencing resource that is expected to resolve to this resource"