## Conformance Rules
The contents of a resource and the formats used to represent resources SHALL conform to the rules described in FHIR specification, as defined in the narrative of the specification, and as controlled by the conformance properties defined at: 

https://www.hl7.org/fhir/conformance-rules.html 

Data elements defined in resources and data types have 3 properties that are directly related to conformance: Cardinality, Is-Modifier, and Must-Support. These interact to place conformance requirements on implementations.