FHIR Extensions Pack
5.3.0 - May 2026 International flag

FHIR Extensions Pack, published by HL7 International / FHIR Infrastructure. This guide is not an authorized publication; it is the continuous build for version 5.3.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/HL7/fhir-extensions/ and changes regularly. See the Directory of published versions

Extension: Reserved Code Space

Official URL: http://hl7.org/fhir/StructureDefinition/codesystem-reservedCodeSpace Version: 5.3.0
Standards status: Draft Maturity Level: 0 Computable Name: ReservedCodeSpace
Other Identifiers: OID:2.16.840.1.113883.4.642.40.97.42.152

This extension is used to describe a set of concept codes that has been allocated by the code system steward for users to create their own codes.

Some code systems reserve part of their code space for private codes that anyone can create and use. Without a way to describe this, validators report such codes as invalid. Validators that check codes against a code system with a reserved code space do not flag codes in that space as invalid because of the code system definition (though they might because of value set considerations), nor do they validate the display or provide definitions for such codes.

This is an draft extension definition; the committee is seeking implementation feedback, and the definition or contents of the extension may change in future versions

Context of Use

This extension may be used on the following element(s)

Usage info

Usages:

  • This Extension is not used by any profiles in this Specification

You can also check for usages in the FHIR IG Statistics

Changes since version 5.3.0:

  • New Content

    • Formal Views of Extension Content

    Description of Profiles, Differentials, Snapshots, and how the XML and JSON presentations work.

    This structure is derived from Extension

    Summary

    Complex Extension: This extension is used to describe a set of concept codes that has been allocated by the code system steward for users to create their own codes.

    • reservedCodeSpace: string: Regular expression to identify the set of concept codes allocated for users of the code system to create their own codes. This value must be a regular expression.
    • description: markdown: Narrative explaining the set of concept codes.

    Maturity: 0

    This structure is derived from Extension

    NameFlagsCard.TypeDescription & Constraints    Filter: doco
    Extension 0..* Extension Set of codes reserved for users to create their own codes
    Extension.extension 1..* Extension Extension
    Extension.Slices for extension Content/Rules for all slices
    Extension.Slices for extension.extension:reservedCodeSpace 1..1 Extension Regular expression for the reserved codes
    Extension.Slices for extension.extension:reservedCodeSpace.extension 0..0 Extension
    Extension.Slices for extension.extension:reservedCodeSpace.url 1..1 uri "reservedCodeSpace"
    Extension.Slices for extension.extension:reservedCodeSpace.value[x] 1..1 string Value of extension
    Extension.Slices for extension.extension:description 0..1 Extension Narrative explaining the set of codes
    Extension.Slices for extension.extension:description.extension 0..0 Extension
    Extension.Slices for extension.extension:description.url 1..1 uri "description"
    Extension.Slices for extension.extension:description.value[x] 1..1 markdown Value of extension
    Extension.url 1..1 uri "http://hl7.org/fhir/StructureDefinition/codesystem-reservedCodeSpace"

    doco Documentation for this format
    NameFlagsCard.TypeDescription & Constraints    Filter: doco
    Extension 0..* Extension Set of codes reserved for users to create their own codes
    Extension.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension 1..* Extension Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:reservedCodeSpace 1..1 Extension Regular expression for the reserved codes
    Extension.Slices for extension.extension:reservedCodeSpace.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension.extension:reservedCodeSpace.extension 0..0 Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:reservedCodeSpace.url 1..1 uri "reservedCodeSpace"
    Extension.Slices for extension.extension:reservedCodeSpace.value[x] 1..1 string Value of extension
    Extension.Slices for extension.extension:description 0..1 Extension Narrative explaining the set of codes
    Extension.Slices for extension.extension:description.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension.extension:description.extension 0..0 Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:description.url 1..1 uri "description"
    Extension.Slices for extension.extension:description.value[x] 1..1 markdown Value of extension
    Extension.url 1..1 uri "http://hl7.org/fhir/StructureDefinition/codesystem-reservedCodeSpace"

    doco Documentation for this format

    This structure is derived from Extension

    Summary

    Complex Extension: This extension is used to describe a set of concept codes that has been allocated by the code system steward for users to create their own codes.

    • reservedCodeSpace: string: Regular expression to identify the set of concept codes allocated for users of the code system to create their own codes. This value must be a regular expression.
    • description: markdown: Narrative explaining the set of concept codes.

    Maturity: 0

    Differential View

    This structure is derived from Extension

    NameFlagsCard.TypeDescription & Constraints    Filter: doco
    Extension 0..* Extension Set of codes reserved for users to create their own codes
    Extension.extension 1..* Extension Extension
    Extension.Slices for extension Content/Rules for all slices
    Extension.Slices for extension.extension:reservedCodeSpace 1..1 Extension Regular expression for the reserved codes
    Extension.Slices for extension.extension:reservedCodeSpace.extension 0..0 Extension
    Extension.Slices for extension.extension:reservedCodeSpace.url 1..1 uri "reservedCodeSpace"
    Extension.Slices for extension.extension:reservedCodeSpace.value[x] 1..1 string Value of extension
    Extension.Slices for extension.extension:description 0..1 Extension Narrative explaining the set of codes
    Extension.Slices for extension.extension:description.extension 0..0 Extension
    Extension.Slices for extension.extension:description.url 1..1 uri "description"
    Extension.Slices for extension.extension:description.value[x] 1..1 markdown Value of extension
    Extension.url 1..1 uri "http://hl7.org/fhir/StructureDefinition/codesystem-reservedCodeSpace"
    Extension.value[x] 0..0 Value of extension

    doco Documentation for this format

    Snapshot View

    NameFlagsCard.TypeDescription & Constraints    Filter: doco
    Extension 0..* Extension Set of codes reserved for users to create their own codes
    Extension.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension 1..* Extension Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:reservedCodeSpace 1..1 Extension Regular expression for the reserved codes
    Extension.Slices for extension.extension:reservedCodeSpace.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension.extension:reservedCodeSpace.extension 0..0 Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:reservedCodeSpace.url 1..1 uri "reservedCodeSpace"
    Extension.Slices for extension.extension:reservedCodeSpace.value[x] 1..1 string Value of extension
    Extension.Slices for extension.extension:description 0..1 Extension Narrative explaining the set of codes
    Extension.Slices for extension.extension:description.id 0..1 id Unique id for inter-element referencing
    Extension.Slices for extension.extension:description.extension 0..0 Extension
    Slice: Unordered, Open by value:url

    Slicing Note: The rules on this element (including its children) apply to all the slices, but are not repeated in them
    Extension.Slices for extension.extension:description.url 1..1 uri "description"
    Extension.Slices for extension.extension:description.value[x] 1..1 markdown Value of extension
    Extension.url 1..1 uri "http://hl7.org/fhir/StructureDefinition/codesystem-reservedCodeSpace"

    doco Documentation for this format

     

    Other representations of profile: CSV, Excel, Schematron

    Constraints

    Id Grade Path(s) Description Expression
    ele-1 error **ALL** elements All FHIR elements must have a @value or children hasValue() or (children().count() > id.count())
    ext-1 error **ALL** extensions Must have either extensions or value[x], not both extension.exists() != value.exists()

    R4B

    The extension is unchanged in R4B

    R4

    The extension is unchanged in R4

    R3

    The extension is unchanged in R3

    Search Parameters for this Extension

    (none found)