A unit that the user may choose when providing a quantity value.

Provide either unitOption(s) or unitValueSet. If either of the extensions are present, the units for a Quantity element are constrained to only the units listed by the extensions - i.e. it is treated as a "required", not an "extensible" binding. In the absence of either, any unit is valid. See additional guidance and examples in the SDC implementation guide. If this extension present and an answer is provided for the question item in the QuestionnaireResponse, then the valueQuantity SHALL have a Quantity.code and Quantity.system that match the Coding.code and system of one of the allowed values if the Coding has a code and/or system. If the Coding only has a display, then the Quantity.unit must match. (Note that Coding with only a display is strongly discouraged.) If there is a match on code and system, but no match on display/unit, systems MAY raise a warning. However, because of translation and bandwidth considerations, some systems MAY opt to drop the unit or express it in an alternate language.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

• unordered
• Open
• discriminators: value:url

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 SHALL be a URI for the Structure Definition defining the extension.

Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).