From Daniel Karlsson (edited):
-------------------------------------
The designation.additionalUse element with multiple Codings will partly support the use case for the proposed extension for designation use for SNOMED CT.  Example:
...
"use": {
"coding":

{ "system" : "http://snomed.info/sct", "code" : "900000000000013009", "display" : "Synonym" }

},
"additionalUse": [

{ "system" : "http://snomed.info/sct", "code" : "900000000000509007", "display" : "US English" }

,

{ "system" : "http://snomed.info/sct", "code" : "900000000000549004", "display" : "Acceptable" }

,

{ "system" : "http://snomed.info/sct", "code" : "900000000000508004", "display" : "GB English" }

,

{ "system" : "http://snomed.info/sct", "code" : "900000000000548007", "display" : "Preferred" }

],
...

But this would not support designations acceptable in one context but preferred in another (as in the example above), which would again require repeating of designations with identical terms (.value).

So, if there are other use cases which .additionalUse aims to support, I guess I have no opinion, but if it is to support SNOMED use, the extension still is preferred. For SNOMED, three elements are required (description type, use context, and acceptability) and while having two is better than one, it does not help with all SNOMED use cases.

I added some of the work I've done with using the DUC extension for extracting information from SNOMED CT on Github: https://github.com/danka74/nll_valuesets

-------------------------------------

This was discussed on the 2022-02-22 SNOMED on FHIR [call](https://confluence.ihtsdotools.org/pages/viewpage.action?pageId=142126275).

If the work on the designation use extension for supporting the needs of SNOMED CT can be incorporated into the proposed updates in FHIR-29821 to add the designation.additionalUse element (e.g., make additionalUse a backbone element with the additional elements needed to support description type, use context, and acceptability?), then this could become a general purpose solution that will be able to meet the needs for this in SNOMED CT as well as other terminologies (including LOINC, ICD, etc. - and likely any others).