id

primitive type

Base StructureDefinition for id type: Any combination of letters, numerals, "-" and ".", with a length limit of 64 characters. (This might be an integer, an unprefixed OID, UUID or any other identifier pattern that meets these constraints.) Ids are case-insensitive.

Official spec

Path	Card.	Type	Description & Constraints
id	0..*	—	Primitive Type id
.id	0..1	String	xml:id (or equivalent in JSON)
.extension	0..*	Extension	Additional content defined by implementations
.value	0..1	String	Primitive value for id