Provides a rendered version of the value intended for human display.  For example, a sensitive identifier (e.g. social security number) partially obscured by asterisks; a drivers licence number with dashes inserted; a date formatted as MMM dd, yyyy; etc.

In some cases, this extension may be present and the value won't be present.  For example if the recipient only has permission to see a partially masked view of a value.  The rendering may be realm-specific.  (E.g. the use of ',' vs. '.' when rendering numbers.).

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).