If present, indicates that this questionnaire has expectations with respect to assembly. Specifically, indicates whether this form requires assembly (i.e. it can't be used directly without invoking the $assemble operation operation on it) and/or whether it is intended for use only as a 'child' in an assembly process. The assembly processs might mean filling in item metadata based on information looked up from item.definitions and/or retrieving sub-questionnaires pointed to by sub-questionnaire extensions.

SDC-conformant Questionnaires SHALL declare this extension if they require an assembly process prior to use. If not declared, then the Questionnaire is not necessarily safe for use as a child form and does not require assembly prior to use.

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

May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• 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).