> ## 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 |


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