For the support,
When an entity type whose has some properties with ConcurrencyCheck attribute, during get request, either single result or collection result, each return result will have "@odata.etag" annotation.
When request return a single entity and this setting is added "configuration.MessageHandlers.Add(new ETagMessageHandler());", the response Header will have Etag Header beside the "@odata.etag" annotation in response body.
During CRUD, If-Match and If-None-Match are checked.
If an item required etag, but during update/delete request, there is no If-Match or If-None-Match tag, should return 428 (precondition required).
Items not covered by above issue and need to be covered by this issue,
Checklist (Uncheck if it is not completed)
Additional work necessary
Need document update on how to use EtagMessageHandler.