Meaning of name
The intention for the property "External formatter URI" was a concise name which highlights two distinct characteristics:
- It is an external formatter which has a formatting attribute ($1 as it is common for message) and it is expected to be external (meaning something outside of the current wiki)
- The URI part hints that the "External formatter" needs to be a URI (aka URL)
"External formatter URI" specific annotation only appears in tandem with the Help:Datatype "External identifier" type and any other use case is not supported.