---
type: "datatype"
title: "Extension"
datatype: "Extension"
---
# Extension

- [Datatypes](/datatypes)
- [Definitions](/datatypes-definitions#Extension)
- [Examples](/datatypes-examples#Extension)
- [Mappings](/datatypes-mappings#Extension)
- [Profiles](/datatypes-profiles#Extension)

## Elements

- **[Extension.@url](/datatypes-definitions#Extension.%40url)** [1..1]: [uri](/uri) Source of the definition for the extension code - a logical name or a URL
- **[Extension.value[x]](/datatypes-definitions#Extension.value%5Bx%5D)** [0..1]: * Value of extension - must be one of a constrained set of the data types (see [Extensibility](extensibility.html) for a list)

## Summary Elements

- **Extension.@url**: In _summary view
- **Extension.value[x]**: In _summary view

## Comments

- **Extension.@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

## Mappings

- **Extension.@url**: RIM Mapping: N/A
- **Extension.value[x]**: RIM Mapping: N/A