FHIR Validator - checking for non required element

Is there a way I can use the FHIR validator to check for an element that isn’t required by the US Core? For example in encounter, encounter.id is optional (0-1). We are receiving files from a vendor, and we expect this to be populated, but the validator isn’t checking for it.

If you define a profile that requires something you can tell the validator to check whether an instance is valid against that profile.