The template table may constrain values or vocabularies to be used with an element or attribute. Value constraints include a conformance verb (SHALL, SHOULD, MAY, etc.) as defined in Section 5.2.5, and specified in the Value Conformance column of the template tables.

Elements for which nullFlavor is forbidden are indicated with an additional constraint keyword noNull.

Additionally, constraints specifying Value Sets include a coding strength conformance CWE (Coded With Extensibility) or CNE (Coded with No Extensibility), as defined in Core Principles and Properties of HL7 Version 3 Models, Release 1.

Further, Value Set constraints can be static, meaning that they are bound to a specified version of a Value Set, or dynamic, meaning that they are bound to the most current version of the Value Set. By default, Value Sets have dynamic binding, unless explicitly specified with an additional constraint keyword static.