reference to HL7 FHIR signature

[TomCJones]

at 2020-01-21 meeting Sal proposed a using signature data from HL7 FHIR signature section.
This was done. BUT
There is an element that they require on the signature where we do not have.
Proposal is to add purpose or "CommitmentTypeIndication" to spec signature. - IT IS NOT RECOMMEND to refer to ASTM E1762-95(2013) which as been withdrawn by ISO and should be removed from FHIR.
quote FHIR "The Signature SHALL include a "CommitmentTypeIndication" element for the Purpose(s) of Signature. The Purpose can be the action being attested to, or the role associated with the signature. The value shall come from ASTM E1762-95(2013). The Signature.type shall contain the same values as the CommitmentTypeIndication element."

[TomCJones]

the change to add a purpose element to the signature was deferred until a more explicit requirement is articulated. Maybe we could find someone who knows why the element was inserted into FHIR. It seems that the document signed would convey the purpose better and in more detail. It would be valuable in each section of the spec to describe the purpose of the signature in each case where it is used.