> ## 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.

# Expression

> Base StructureDefinition for Expression Type: A expression that is evaluated in a specified context and returns a value. The context of use of the expression must specify the context in which the expression is evaluated, and how the result of the expression is used.

## 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 |
| description | No | string | Natural language description of the condition |
| name | No | id | Short name assigned to expression for reuse |
| language | Yes | code | text/cql / text/fhirpath / application/x-fhir-query / etc. |
| expression | No | string | Expression in specified language |
| reference | No | uri | Where the expression is found |


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