The JSON structure definition for structuredefinition-fhir-type has several variations from what is displayed on the page: http://hl7.org/fhir/2021Mar/extension-structuredefinition-fhir-type.html , and both have several differences from the R4 version here. Some of these change I believe are replicated on many resources, but I don't know if I will have time to make tooling to search for them or not (if I do, I will link that ticket to this one).

R4 -> R4B changes specific to this extension (constraint ele-1):

• expression added or $this is Parameters
• human added unless an empty Parameters resource
• xpath added |self::f:Parameters

General changes (believe to be on other definitions):

• R4B extensions are listed with valueUri instead of the R4 versions with valueUrl