FHIR Extensions Pack
5.2.0 - February 2025 International flag

This page is part of the FHIR Core Extensions Registry (v5.2.0: Release 5.2) based on FHIR (HL7® FHIR® Standard) v5.0.0. This is the current published version. For a full list of available versions, see the Directory of published versions

Extension: Allele - Detailed Descriptions

Page standards status: Deprecated Maturity Level: 1

Definitions for the observation-geneticsAllele extension.

Guidance on how to interpret the contents of this table can be found here

0. Extension
Definition

Allele information.


Optional Extension Element - found in all resources.

ShortAlleleOptional Extensions Element
Control0..1*
Is Modifierfalse
Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
2. Extension.extension:Name
Slice NameName
Definition

An allele is one of a set of coexisting sequence variants of a gene (SO:0001023). This element is the common name for the allele. LOINC Code: (48008-7).

ShortName of alleleAdditional content defined by implementations
Control0..1*
TypeExtension
Is Modifierfalse
Summaryfalse
Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
4. Extension.extension:Name.extension
Definition

An Extension


May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and managable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

ShortExtensionAdditional content defined by implementations
Comments

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

Control0..0*
TypeExtension
Is Modifierfalse
Summaryfalse
Alternate Namesextensions, user content
Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
  • value @ url
  • 6. Extension.extension:Name.url
    Definition

    Source of the definition for the extension code - a logical name or a URL.

    Shortidentifies the meaning of the extension
    Comments

    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.

    Control1..1
    Typeuri
    Is Modifierfalse
    Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
    XML FormatIn the XML format, this property is represented as an attribute.
    Summaryfalse
    Fixed ValueName
    8. Extension.extension:Name.value[x]
    Definition

    Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

    ShortValue of extension
    Control10..1
    This element is affected by the following invariants: ext-1
    Binding

    EMBL-EBI database of AlleleName.

    TypeCodeableConcept, date, Meta, Address, Attachment, integer, Count, DataRequirement, Dosage, uuid, Identifier, RatioRange, Coding, SampledData, id, positiveInt, Distance, Availability, integer64, Period, Duration, canonical, Range, RelatedArtifact, base64Binary, UsageContext, Timing, decimal, ExtendedContactDetail, ParameterDefinition, dateTime, code, string, oid, instant, ContactPoint, HumanName, Money, markdown, Ratio, Age, Reference, TriggerDefinition, Quantity, uri, url, Annotation, ContactDetail, boolean, Expression, CodeableReference, Signature, unsignedInt, time
    [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
    Is Modifierfalse
    Summaryfalse
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    10. Extension.extension:State
    Slice NameState
    Definition

    The level of occurrence of a single DNA Sequence Variant within a set of chromosomes. Heterozygous indicates the DNA sequence variant is only present in one of the two genes contained in homologous chromosomes. Homozygous indicates the DNA Sequence Variant is present in both genes contained in homologous chromosomes. Hemizygous indicates the DNA Sequence Variant exists in the only single copy of a gene in a non-homologous chromosome (the male X and Y chromosome are non-homologous). Hemiplasmic indicates that the DNA Sequence Variant is present in some but not all of the copies of mitochondrial DNA. Homoplasmic indicates that the DNA Sequence Variant is present in all of the copies of mitochondrial DNA. LOINC Code: (53034-5).

    ShortThe level of occurrence of a single DNA sequence variant within a set of chromosomes: Heteroplasmic / Homoplasmic / Homozygous / Heterozygous / HemizygousAdditional content defined by implementations
    Control0..1*
    TypeExtension
    Is Modifierfalse
    Summaryfalse
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
    12. Extension.extension:State.extension
    Definition

    An Extension


    May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and managable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

    ShortExtensionAdditional content defined by implementations
    Comments

    There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

    Control0..0*
    TypeExtension
    Is Modifierfalse
    Summaryfalse
    Alternate Namesextensions, user content
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
    SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
    • value @ url
    • 14. Extension.extension:State.url
      Definition

      Source of the definition for the extension code - a logical name or a URL.

      Shortidentifies the meaning of the extension
      Comments

      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.

      Control1..1
      Typeuri
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      XML FormatIn the XML format, this property is represented as an attribute.
      Summaryfalse
      Fixed ValueState
      16. Extension.extension:State.value[x]
      Definition

      Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

      ShortValue of extension
      Control10..1
      This element is affected by the following invariants: ext-1
      TypeCodeableConcept, date, Meta, Address, Attachment, integer, Count, DataRequirement, Dosage, uuid, Identifier, RatioRange, Coding, SampledData, id, positiveInt, Distance, Availability, integer64, Period, Duration, canonical, Range, RelatedArtifact, base64Binary, UsageContext, Timing, decimal, ExtendedContactDetail, ParameterDefinition, dateTime, code, string, oid, instant, ContactPoint, HumanName, Money, markdown, Ratio, Age, Reference, TriggerDefinition, Quantity, uri, url, Annotation, ContactDetail, boolean, Expression, CodeableReference, Signature, unsignedInt, time
      [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
      Is Modifierfalse
      Summaryfalse
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      18. Extension.extension:Frequency
      Slice NameFrequency
      Definition

      A physical quality which inheres to the allele by virtue of the number instances of the allele within a population. LOINC Code: (81258-6).

      ShortAllele frequencyAdditional content defined by implementations
      Control0..1*
      TypeExtension
      Is Modifierfalse
      Summaryfalse
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
      20. Extension.extension:Frequency.extension
      Definition

      An Extension


      May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and managable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

      ShortExtensionAdditional content defined by implementations
      Comments

      There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

      Control0..0*
      TypeExtension
      Is Modifierfalse
      Summaryfalse
      Alternate Namesextensions, user content
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
      SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
      • value @ url
      • 22. Extension.extension:Frequency.url
        Definition

        Source of the definition for the extension code - a logical name or a URL.

        Shortidentifies the meaning of the extension
        Comments

        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.

        Control1..1
        Typeuri
        Is Modifierfalse
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        XML FormatIn the XML format, this property is represented as an attribute.
        Summaryfalse
        Fixed ValueFrequency
        24. Extension.extension:Frequency.value[x]
        Definition

        Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

        ShortValue of extension
        Control10..1
        This element is affected by the following invariants: ext-1
        Typedecimal, date, Meta, Address, Attachment, integer, Count, DataRequirement, Dosage, uuid, Identifier, RatioRange, Coding, SampledData, id, positiveInt, Distance, Availability, integer64, Period, Duration, canonical, Range, RelatedArtifact, base64Binary, UsageContext, Timing, ExtendedContactDetail, CodeableConcept, ParameterDefinition, dateTime, code, string, oid, instant, ContactPoint, HumanName, Money, markdown, Ratio, Age, Reference, TriggerDefinition, Quantity, uri, url, Annotation, ContactDetail, boolean, Expression, CodeableReference, Signature, unsignedInt, time
        [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
        Is Modifierfalse
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        Summaryfalse
        Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
        26. Extension.url
        Definition

        Source of the definition for the extension code - a logical name or a URL.

        Shortidentifies the meaning of the extension
        Comments

        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.

        Control1..1
        Typeuri
        Is Modifierfalse
        XML FormatIn the XML format, this property is represented as an attribute.
        Summaryfalse
        Fixed Valuehttp://hl7.org/fhir/StructureDefinition/observation-geneticsAllele
        28. Extension.value[x]
        Definition

        Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

        ShortValue of extension
        Control0..01
        This element is affected by the following invariants: ext-1
        TypeChoice of: base64Binary, boolean, canonical, code, date, dateTime, decimal, id, instant, integer, integer64, markdown, oid, positiveInt, string, time, unsignedInt, uri, url, uuid, Address, Age, Annotation, Attachment, CodeableConcept, CodeableReference, Coding, ContactPoint, Count, Distance, Duration, HumanName, Identifier, Money, Period, Quantity, Range, Ratio, RatioRange, Reference, SampledData, Signature, Timing, ContactDetail, DataRequirement, Expression, ParameterDefinition, RelatedArtifact, TriggerDefinition, UsageContext, Availability, ExtendedContactDetail, Dosage, Meta
        Is Modifierfalse
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        Summaryfalse
        Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))

        Guidance on how to interpret the contents of this table can be found here

        0. Extension
        Definition

        Allele information.

        ShortAllele
        Control0..1
        2. Extension.extension:Name
        Slice NameName
        Definition

        An allele is one of a set of coexisting sequence variants of a gene (SO:0001023). This element is the common name for the allele. LOINC Code: (48008-7).

        ShortName of allele
        Control0..1
        TypeExtension
        4. Extension.extension:Name.extension
        Control0..0
        6. Extension.extension:Name.url
        Typeuri
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        Fixed ValueName
        8. Extension.extension:Name.value[x]
        Control1..?
        Binding

        EMBL-EBI database of AlleleName.

        TypeCodeableConcept
        [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
        10. Extension.extension:State
        Slice NameState
        Definition

        The level of occurrence of a single DNA Sequence Variant within a set of chromosomes. Heterozygous indicates the DNA sequence variant is only present in one of the two genes contained in homologous chromosomes. Homozygous indicates the DNA Sequence Variant is present in both genes contained in homologous chromosomes. Hemizygous indicates the DNA Sequence Variant exists in the only single copy of a gene in a non-homologous chromosome (the male X and Y chromosome are non-homologous). Hemiplasmic indicates that the DNA Sequence Variant is present in some but not all of the copies of mitochondrial DNA. Homoplasmic indicates that the DNA Sequence Variant is present in all of the copies of mitochondrial DNA. LOINC Code: (53034-5).

        ShortThe level of occurrence of a single DNA sequence variant within a set of chromosomes: Heteroplasmic / Homoplasmic / Homozygous / Heterozygous / Hemizygous
        Control0..1
        TypeExtension
        12. Extension.extension:State.extension
        Control0..0
        14. Extension.extension:State.url
        Typeuri
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        Fixed ValueState
        16. Extension.extension:State.value[x]
        Control1..?
        TypeCodeableConcept
        [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
        18. Extension.extension:Frequency
        Slice NameFrequency
        Definition

        A physical quality which inheres to the allele by virtue of the number instances of the allele within a population. LOINC Code: (81258-6).

        ShortAllele frequency
        Control0..1
        TypeExtension
        20. Extension.extension:Frequency.extension
        Control0..0
        22. Extension.extension:Frequency.url
        Typeuri
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        Fixed ValueFrequency
        24. Extension.extension:Frequency.value[x]
        Control1..?
        Typedecimal
        [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
        Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
        26. Extension.url
        Fixed Valuehttp://hl7.org/fhir/StructureDefinition/observation-geneticsAllele
        28. Extension.value[x]
        Control0..0

        Guidance on how to interpret the contents of this table can be found here

        0. Extension
        Definition

        Allele information.

        ShortAllele
        Control0..1
        Is Modifierfalse
        Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
        ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
        2. Extension.id
        Definition

        Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

        ShortUnique id for inter-element referencing
        Control0..1
        This element is affected by the following invariants: ele-1
        Typeid
        Is Modifierfalse
        XML FormatIn the XML format, this property is represented as an attribute.
        Summaryfalse
        4. Extension.extension
        Definition

        May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and managable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

        ShortAdditional content defined by implementations
        Comments

        There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

        Control0..*
        TypeExtension
        Is Modifierfalse
        Summaryfalse
        Alternate Namesextensions, user content
        Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
        ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
        SlicingThis element introduces a set of slices on Extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
        • value @ url
        • 6. Extension.extension:Name
          Slice NameName
          Definition

          An allele is one of a set of coexisting sequence variants of a gene (SO:0001023). This element is the common name for the allele. LOINC Code: (48008-7).

          ShortName of allele
          Control0..1
          TypeExtension
          Is Modifierfalse
          Summaryfalse
          Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
          ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
          8. Extension.extension:Name.id
          Definition

          Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

          ShortUnique id for inter-element referencing
          Control0..1
          This element is affected by the following invariants: ele-1
          Typeid
          Is Modifierfalse
          XML FormatIn the XML format, this property is represented as an attribute.
          Summaryfalse
          10. Extension.extension:Name.extension
          Definition

          An Extension

          ShortExtension
          Control0..0
          TypeExtension
          Is Modifierfalse
          Summaryfalse
          Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
          ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
          SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
          • value @ url
          • 12. Extension.extension:Name.url
            Definition

            Source of the definition for the extension code - a logical name or a URL.

            Shortidentifies the meaning of the extension
            Comments

            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.

            Control1..1
            Typeuri
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            XML FormatIn the XML format, this property is represented as an attribute.
            Summaryfalse
            Fixed ValueName
            14. Extension.extension:Name.value[x]
            Definition

            Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

            ShortValue of extension
            Control1..1
            This element is affected by the following invariants: ext-1
            Binding

            EMBL-EBI database of AlleleName.

            TypeCodeableConcept
            [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
            Is Modifierfalse
            Summaryfalse
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            16. Extension.extension:State
            Slice NameState
            Definition

            The level of occurrence of a single DNA Sequence Variant within a set of chromosomes. Heterozygous indicates the DNA sequence variant is only present in one of the two genes contained in homologous chromosomes. Homozygous indicates the DNA Sequence Variant is present in both genes contained in homologous chromosomes. Hemizygous indicates the DNA Sequence Variant exists in the only single copy of a gene in a non-homologous chromosome (the male X and Y chromosome are non-homologous). Hemiplasmic indicates that the DNA Sequence Variant is present in some but not all of the copies of mitochondrial DNA. Homoplasmic indicates that the DNA Sequence Variant is present in all of the copies of mitochondrial DNA. LOINC Code: (53034-5).

            ShortThe level of occurrence of a single DNA sequence variant within a set of chromosomes: Heteroplasmic / Homoplasmic / Homozygous / Heterozygous / Hemizygous
            Control0..1
            TypeExtension
            Is Modifierfalse
            Summaryfalse
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
            18. Extension.extension:State.id
            Definition

            Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

            ShortUnique id for inter-element referencing
            Control0..1
            This element is affected by the following invariants: ele-1
            Typeid
            Is Modifierfalse
            XML FormatIn the XML format, this property is represented as an attribute.
            Summaryfalse
            20. Extension.extension:State.extension
            Definition

            An Extension

            ShortExtension
            Control0..0
            TypeExtension
            Is Modifierfalse
            Summaryfalse
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
            SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
            • value @ url
            • 22. Extension.extension:State.url
              Definition

              Source of the definition for the extension code - a logical name or a URL.

              Shortidentifies the meaning of the extension
              Comments

              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.

              Control1..1
              Typeuri
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              XML FormatIn the XML format, this property is represented as an attribute.
              Summaryfalse
              Fixed ValueState
              24. Extension.extension:State.value[x]
              Definition

              Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

              ShortValue of extension
              Control1..1
              This element is affected by the following invariants: ext-1
              TypeCodeableConcept
              [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              26. Extension.extension:Frequency
              Slice NameFrequency
              Definition

              A physical quality which inheres to the allele by virtue of the number instances of the allele within a population. LOINC Code: (81258-6).

              ShortAllele frequency
              Control0..1
              TypeExtension
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
              28. Extension.extension:Frequency.id
              Definition

              Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

              ShortUnique id for inter-element referencing
              Control0..1
              This element is affected by the following invariants: ele-1
              Typeid
              Is Modifierfalse
              XML FormatIn the XML format, this property is represented as an attribute.
              Summaryfalse
              30. Extension.extension:Frequency.extension
              Definition

              An Extension

              ShortExtension
              Control0..0
              TypeExtension
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
              SlicingThis element introduces a set of slices on Extension.extension.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
              • value @ url
              • 32. Extension.extension:Frequency.url
                Definition

                Source of the definition for the extension code - a logical name or a URL.

                Shortidentifies the meaning of the extension
                Comments

                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.

                Control1..1
                Typeuri
                Is Modifierfalse
                Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
                XML FormatIn the XML format, this property is represented as an attribute.
                Summaryfalse
                Fixed ValueFrequency
                34. Extension.extension:Frequency.value[x]
                Definition

                Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

                ShortValue of extension
                Control1..1
                This element is affected by the following invariants: ext-1
                Typedecimal
                [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
                Is Modifierfalse
                Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
                Summaryfalse
                Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
                36. Extension.url
                Definition

                Source of the definition for the extension code - a logical name or a URL.

                Shortidentifies the meaning of the extension
                Comments

                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.

                Control1..1
                Typeuri
                Is Modifierfalse
                XML FormatIn the XML format, this property is represented as an attribute.
                Summaryfalse
                Fixed Valuehttp://hl7.org/fhir/StructureDefinition/observation-geneticsAllele
                38. Extension.value[x]
                Definition

                Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).

                ShortValue of extension
                Control0..0
                This element is affected by the following invariants: ext-1
                TypeChoice of: base64Binary, boolean, canonical, code, date, dateTime, decimal, id, instant, integer, integer64, markdown, oid, positiveInt, string, time, unsignedInt, uri, url, uuid, Address, Age, Annotation, Attachment, CodeableConcept, CodeableReference, Coding, ContactPoint, Count, Distance, Duration, HumanName, Identifier, Money, Period, Quantity, Range, Ratio, RatioRange, Reference, SampledData, Signature, Timing, ContactDetail, DataRequirement, Expression, ParameterDefinition, RelatedArtifact, TriggerDefinition, UsageContext, Availability, ExtendedContactDetail, Dosage, Meta
                Is Modifierfalse
                Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
                Summaryfalse
                Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))