Record of someone or something involvement in an activity or event.

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

An entity (usually a Practitioner, Patient, or Organization but potentially a device or other entity) that participates in a healthcare task or activity. The participant is not necessarily the performer, and the role (ParticipationType), the ParticipationPeriod, and other details of the participation are by the Participation structure.

The role played by the participant engaged in the action, for example, as the attending physician, surgical assistant, etc.

The point in time or span of time the participant is involved.

The party represented by the actual participant.

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).