Primitive type 'oid'
A globally unique string representing an ISO Object Identifier (OID) in a form that consists only of numbers and dots (e.g., '2.16.840.1.113883.3.1').
Note that FHIR strings SHALL NOT exceed 1,048,576 (1024*1024) characters in size
All FHIR elements must have a @value or children
hasValue() or (children().count() > id.count())
Must conform to OID (#.#.#), UUID (32 hexadecimal digits separated by hyphens), or RUID (a letter followed by any combination of letters, numbers or hyphens)
unique id for the element within a resource (for internal references)
Must have either extensions or value[x], not both