Purpose and usage of DocumentReference.date are unclear

[simoneOnFhir]

What is the motivation behind the 1..1 cardinality on DocumentReference.date?
I couldn't find any mapping to XDS, so I wonder why this decision was made...

date is also listed among the optional search parameters for ITI-67, but again, there is no mapping to an equivalent XDS-parameter.

Note 5 on the mapping of the creationparameter "The FHIR DocumentReference does not yet have a query parameter for creationTime of the document, it has only a date element which is the creation date/time of the DocumentReference. For FHIR R4 we align these two elements so that query will function." makes a reference to date which is presumably out of date, since no apparent alignment has occured in R4, but the creation parameter is non the less currently functional as a custom parameter.
Is it possible that date is a remnant of the 'before times', when the creation search didn't work...?

See discussion in Zulip: https://chat.fhir.org/#narrow/stream/179223-ihe/topic/DocumentReference.2Edate.201.2E.2E1

[JohnMoehrke]

I can't find a justification. i think it is from the STU3 days where we used the .date because there was no actual creation date/time that was available to be queried. Where as now we added the DocumentReference-Creation search parameter.

seems like it is still a useful element, just not anything that should be mandated.

[JohnMoehrke]

remove the constraint in comprehensive document reference.