The FHIRPath spec describes that FHIRPath paths can be prefixed by a concrete type to ensure the path will only match instances rooted in that type (http://hl7.org/fhirpath/#path-selection). E.g. Patient.name.family It's unclear however, that these types need not be concrete and may be superclasses, matching all of the subtypes, e.g. Resource.meta.

The FHIRPath team thinks this is FHIR specific, and this kind of functionality should be described in the FHIR appendix to FHIRPath (http://build.fhir.org/fhirpath.html).

I don't know whether I agree, but in any case we should document this explicitly somewhere.