> ## Documentation Index
> Fetch the complete documentation index at: https://docs.metriport.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Coding

> Base StructureDefinition for Coding Type: A reference to a code defined by a terminology system.

## Properties

| Name         | Required | Type                                                   | Description                                    |
| ------------ | -------- | ------------------------------------------------------ | ---------------------------------------------- |
| id           | No       | string                                                 | Unique id for inter-element referencing        |
| extension    | No       | [Extension](/medical-api/fhir/data-types/extension)\[] | Additional content defined by implementations  |
| system       | No       | uri                                                    | Identity of the terminology system             |
| version      | No       | string                                                 | Version of the system - if relevant            |
| code         | No       | code                                                   | Symbol in syntax defined by the system         |
| display      | No       | string                                                 | Representation defined by the system           |
| userSelected | No       | boolean                                                | If this coding was chosen directly by the user |