In some cases it might make sense to invoke an operation while providing resource content directly. For example, a hypothetical decision support operation like "/$schedule-appointment" might take in a set of resource references like: which patient and which provider(s) (in addition to, say, a period of dates).

But other operations would take resources directly, rather than refernces. For example, the existing $validate operation takes an input:

resource0..1Resource Must be present unles the mode is "delete"

Does this mean that a resource is posted? Or a reference to a resource? Context suggests that the actual resource body would be POSTed here, but I can't see how the spec says this.

It would be good to have a way to pass in resource values or resource references. Or to have parameters explicitly identified as "value" vs. "reference" types. Or, really, anything to clarify this ambiguity.

—

On this same subject, I'm also puzzled about the difference between OperationDefinition.parameter.type

<type value="Resource"/> \\vs.
<type value="Any"/>

(Former appears at http://hl7-fhir.github.io/resource-operations.html#validate, while latter appears at http://hl7-fhir.github.io/questionnaire-operations.html#populate). Do these mean something different?