Indicates that the evaluation should be performed as though it was the given date and time. The most direct implication of this is that references to "Now" within the evaluation logic of the module should result in this value. In addition, wherever possible, the data accessed by the module should appear as though it was accessed at this time. The evaluateAtDateTime value may be any time in the past or future, enabling both retrospective and prospective scenarios. If no value is provided, the requestDateTime is assumed.

unique id for the element within a resource (for internal references).

An Extension

Source of the definition for the extension code - a logical name or a URL.

The definition may point directly to a computable or human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition should be version specific. This will ideally be the URI for the Resource Profile defining the extension, with the code for the extension after a #.

Value of extension - may be a resource or one of a constrained set of the data types (see Extensibility in the spec for list).