When saving or updating resources, one or several identifier values are often provided (Identifier.value) to universally identify the resource. At this point, it would be good to be able to validate that the identifier value that is provided is valid before saving it. 

As identifier systems can be represented as NamingSystem resources, it would be good to have a simple operation to just validate an identifier value within that naming system (by provding the identifier value and identifier system). 

Perhaps the NamingSystem resource could also be extended with elements for specifying validation rules. From my experience, the majority of business identifiers have some type of required format. 

See this discussion in the FHIR chat:
https://chat.fhir.org/#narrow/stream/179166-implementers/topic/Validating.20business.20identifiers