Captures constraints on each element within the resource, profile, or extension.

The path identifies the element and is expressed as a "."-separated list of ancestor elements, beginning with the name of the resource or extension.

Codes that define how this element is represented in instances, when the deviation varies from the normal case.

In resources, this is rarely used except for special cases where the representation deviates from the normal, and can only be done in the base standard (and profiles must reproduce what the base standard does). This element is used quite commonly in Logical models when the logical models represent a specific serialization format (e.g. CDA, v2 etc).

The name of this element definition slice, when slicing is working. The name must be a token with no dots or spaces. This is a unique name referring to a specific set of constraints applied to this element, used to provide a name to different slices of the same element.

May also be used for code generation purposes.

The name SHALL be unique within the structure within the context of the constrained resource element. (Though to avoid confusion, uniqueness across all elements is recommended.).

A single preferred label which is the text to display beside the element indicating its meaning or to use to prompt for the element in a user display or form.

See also the extension (http://hl7.org/fhir/StructureDefinition/elementdefinition-question)[extension-elementdefinition-question.html].

A code that has the same meaning as the element in a particular terminology.

Links the meaning of an element to an external terminology, and is very useful for searching and indexing.

The concept SHALL be properly aligned with the data element definition and other constraints, as defined in the code system, including relationships, of any code listed here. Where multiple codes exist in a terminology that could correspond to the data element, the most granular code(s) should be selected, so long as they are not more restrictive than the data element itself. The mappings may be used to provide more or less granular or structured equivalences in the code system.

Indicates that the element is sliced into a set of alternative definitions (i.e. in a structure definition, there are multiple different constraints on a single element in the base resource). Slicing can be used in any resource that has cardinality ..* on the base resource, or any resource with a choice of types. The set of slices is any elements that come after this in the element sequence that have the same path, until a shorter path occurs (the shorter path terminates the set).

The first element in the sequence, the one that carries the slicing, is the definition that applies to all the slices. This is based on the unconstrained element, but can apply any constraints as appropriate. This may include the common constraints on the children of the element.

Designates which child elements are used to discriminate between the slices when processing an instance. If one or more discriminators are provided, the value of the child elements in the instance data SHALL completely distinguish which slice the element in the resource matches based on the allowed values for those elements in each of the slices.

If there is no discriminator, the content is hard to process, so this should be avoided. If the base element has a cardinality of ..1, and there is a choice of types, the discriminator must be "@type".

How the element value is interpreted when discrimination is evaluated.

A FHIRPath expression, using a restricted subset of FHIRPath, that is used to identify the element on which discrimination is based.

The only FHIRPath functions that are allowed are resolve(), and extension(url).

A human-readable text description of how the slicing works. If there is no discriminator, this is required to be present to provide whatever information is possible about how the slices can be differentiated.

If it's really not possible to differentiate them, the design should be re-evaluated to make the content usable.

If the matching elements have to occur in the same order as defined in the profile.

Order should only be required when it is a pressing concern for presentation. Profile authors should consider making the order a feature of the rules about the narrative, not the rules about the data - requiring ordered data makes the profile much less re-usable.

Whether additional slices are allowed or not. When the slices are ordered, profile authors can also say that additional slices are only allowed at the end.

Allowing additional elements makes for a much for flexible template - it's open for use in wider contexts, but also means that the content of the resource is not closed, and applications have to decide how to handle content not described by the profile.

A concise description of what this element means (e.g. for use in autogenerated summaries).

May change the term to provide language more appropriate to the context of the profile or to reflect slicing.

Provides a complete explanation of the meaning of the data element for human readability. For the case of elements derived from existing elements (e.g. constraints), the definition SHALL be consistent with the base definition, but convey the meaning of the element in the particular context of use of the resource.

To allow a user to state the usage of an element in a particular context.

It is easy for a different definition to change the meaning of an element and this can have nasty downstream consequences. Please be careful when providing definitions.

Explanatory notes and implementation guidance about the data element, including notes about how to use the data properly, exceptions to proper use, etc.

If it is possible to capture usage rules using constraints, that mechanism should be used in preference to this element.

This element is for traceability of why the element was created and why the constraints exist as they do. This may be used to point to source materials or specifications that drove the structure of this element.

This element does not describe the usage of the element (that's done in comments), rather it's for traceability of why the element is either needed or why the constraints exist as they do. This may be used to point to source materials or specifications that drove the structure of this data element.

Identifies additional names by which this element might also be known.

Allows for better easier recognition of the element by multiple communities, including international communities.

The minimum number of times this element SHALL appear in the instance.

The maximum number of times this element is permitted to appear in the instance.

Information about the base definition of the element, provided to make it unnecessary for tools to trace the deviation of the element through the derived and related profiles. This information is provided when the element definition is not the original definition of an element - i.g. either in a constraint on another type, or for elements from a super type in a snap shot.

The base information does not carry any information that could not be determined from the path and related profiles, but making this determination requires both that the related profiles are available, and that the algorithm to determine them be available. So they are deformalised into this location for tooling convenience, and to ensure that the base information is available without dependencies.

The Path that identifies the base element - this matches the ElementDefinition.path for that element. Across FHIR, there is only one base definition of any element - that is, an element definition on a StructureDefinition without a StructureDefinition.base.

Minimum cardinality of the base element identified by the path.

This is provided for consistency with max, and may affect code generation of mandatory elements of the base resource are generated differently (some reference implementations have done this).

Maximum cardinality of the base element identified by the path.

This is provided to code generation, since the serialization representation in JSON differs depending on whether the base element has max > 1. Also, some forms of code generation may differ.

Identifies the identity of an element defined elsewhere in the profile whose content rules should be applied to the current element.

The data type or resource that the value of this element is permitted to be.

The Type of the element can be left blank in a differential constraint, in which case the type is inherited from the resource. Abstract types are not permitted to appear as a type when multiple types are listed. (I.e. Abstract types cannot be part of a choice).

URL of Data type or Resource that is a(or the) type used for this element. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition e.g. "string" is a reference to http://hl7.org/fhir/StructureDefinition/string. Absolute URLs are only allowed in logical models.

If the element is a reference to another resource, this element contains "Reference", and the targetProfile element defines what resources can be referenced. The targetProfile may be a reference to the general definition of a resource (e.g. http://hl7.org/fhir/StructureDefinition/Patient). There would be one pair of type/code for each allowed target resource type.

Identifies a profile structure or implementation Guide that SHALL hold for the datatype this element refers to. Can be a local reference - to a contained StructureDefinition, or a reference to another StructureDefinition or Implementation Guide by a canonical URL. When an implementation guide is specified, the type SHALL conform to at least one profile defined in the implementation guide.

Used when the type is "Reference", and Identifies a profile structure or implementation Guide that SHALL be true for the target of the reference this element refers to. Can be a local reference - to a contained StructureDefinition, or a reference to another StructureDefinition or Implementation Guide by a canonical URL. When an implementation guide is specified, the target resource SHALL conform to at least one profile defined in the implementation guide.

If the type is a reference to another resource, how the resource is or can be aggregated - is it a contained resource, or a reference, and if the context is a bundle, is it included in the bundle.

Whether this reference needs to be version specific or version independent, or whether either can be used.

The base specification never makes a rule as to which form is allowed, but implementation guides may do this.

The value that should be used if there is no value stated in the instance (e.g. 'if not otherwise specified, the abstract is false').

Default values can only be specified on a resource, data type, or extension definition, and never in a profile that applies to one of these. Specifying a default value means that the property can never been unknown - it must always have a value. Further, the default value can never be changed. For these reasons, default values are (and should be) used extremely sparingly.

The Implicit meaning that is to be understood when this element is missing (e.g. 'when this element is missing, the period is ongoing'.

Implicit meanings for missing values can only be specified on a resource, data type, or extension definition, and never in a profile that applies to one of these. An implicit meaning for a missing value can never be changed, and specifying one has the consequence that constraining its use in profiles eliminates use cases as possibilities, not merely moving them out of scope.

If present, indicates that the order of the repeating element has meaning and describes what that meaning is. If absent, it means that the order of the element has no meaning.

This element can only be asserted on repeating elements and can only be introduced when defining resources or data types. It can be further refined profiled elements but if absent in the base type, a profile cannot assert meaning.

Specifies a value that SHALL be exactly the value for this element in the instance. For purposes of comparison, non-significant whitespace is ignored, and all values must be an exact match (case and accent sensitive). Missing elements/attributes must also be missing.

This is not recommended for Coding and CodeableConcept since these often have highly contextual properties such as version or display.

Specifies a value that the value in the instance SHALL follow - that is, any value in the pattern must be found in the instance. Other additional values may be found too. This is effectively constraint by example. The values of elements present in the pattern must match exactly (case-sensitive, accent-sensitive, etc.).

Mostly used for fixing values of CodeableConcept. At present, pattern[x] is not recommended as a basis for slicing while issues related to this are investigated during the STU period.

A sample value for this element demonstrating the type of information that would typically be found in the element.

Examples will most commonly be present for data where it's not implicitly obvious from either the data type or value set what the values might be. (I.e. Example values for dates or quantities would generally be unnecessary.) If the example value is fully populated, the publication tool can generate an instance automatically.

Describes the purpose of this example amoung the set of examples.

The actual value for the element, which must be one of the types allowed for this element.

The minimum allowed value for the element. The value is inclusive. This is allowed for the types date, dateTime, instant, time, decimal, integer, and Quantity.

Except for date/date/instant, the type of the minValue[x] SHALL be the same as the specified type of the element. For the date/dateTime/instant values, the type of minValue[x] SHALL be either the same, or a a Duration which specifies a relative time limit to the current time. The duration value is positive, and is subtracted from the current clock to determine the minimum allowable value. A minimum value for a Quantity is interpreted as an canonical minimum - e.g. you cannot provide 100mg if the minimum value is 10g.

The maximum allowed value for the element. The value is inclusive. This is allowed for the types date, dateTime, instant, time, decimal, integer, and Quantity.

Except for date/date/instant, the type of the maxValue[x] SHALL be the same as the specified type of the element. For the date/dateTime/instant values, the type of maxValue[x] SHALL be either the same, or a a Duration which specifies a relative time limit to the current time. The duration value is positive, and is added to the current clock to determine the maximum allowable value. A maximum value for a Quantity is interpreted as an canonical maximum - e.g. you cannot provide 10g if the maximum value is 50mg.

Indicates the maximum length in characters that is permitted to be present in conformant instances and which is expected to be supported by conformant consumers that support the element.

Receivers are not required to reject instances that exceed the maximum length. The full length could be stored. In some cases, data might be truncated, though truncation should be undertaken with care and an understanding of the consequences of doing so. If not specified, there is no conformance expectation for length support.

A reference to an invariant that may make additional statements about the cardinality or value in the instance.

Formal constraints such as co-occurrence and other constraints that can be computationally evaluated within the context of the instance.

Constraints should be declared on the "context" element - the lowest element in the hierarchy that is common to all nodes referenced by the constraint.

Allows identification of which elements have their cardinalities impacted by the constraint. Will not be referenced for constraints that do not affect cardinality.

Description of why this constraint is necessary or appropriate.

To be used if the reason for the constraint might not be intuitive to all implementers.

Identifies the impact constraint violation has on the conformance of the instance.

This allows constraints to be asserted as "shall" (error) and "should" (warning).

Text that can be used to describe the constraint in messages identifying that the constraint has been violated.

Should be expressed in business terms as much as possible.

A FHIRPath expression of constraint that can be executed to see if this constraint is met.

Used by validation tooling tests of the validity of the resource.

An XPath expression of constraint that can be executed to see if this constraint is met.

Used in Schematron tests of the validity of the resource.

Elements SHALL use "f" as the namespace prefix for the FHIR namespace, and "x" for the xhtml namespace, and SHALL NOT use any other prefixes.

Note: we are considering deprecating the xpath element. Implementer feedback is welcome.

A reference to the original source of the constraint, for traceability purposes.

This is used when, e.g. rendering, where it is not useful to present inherited constraints when rendering the snapshot.

If true, implementations that produce or consume resources SHALL provide "support" for the element in some meaningful way. If false, the element may be ignored and not supported.

Allows a profile to set expectations for system capabilities beyond merely respecting cardinality constraints.

"Something useful" is context dependent and impossible to describe in the base FHIR specification. For this reason, tue mustSupport flag is never set to true by the FHIR specification itself - it is only set to true in profiles.

This is done in Resource Profiles, where the profile labels an element as mustSupport=true. When a profile does this, it SHALL also make clear exactly what kind of "support" is required, as this can mean many things.

Note that an element that has the property IsModifier is not necessarily a "key" element (e.g. one of the important elements to make use of the resource), nor is it automatically mustSupport - however both of these things are more likely to be true for IsModifier elements than for other elements.

If true, the value of this element affects the interpretation of the element or resource that contains it, and the value of the element cannot be ignored. Typically, this is used for status, negation and qualification codes. The effect of this is that the element cannot be ignored by systems: they SHALL either recognize the element and process it, and/or a pre-determination has been made that it is not relevant to their particular system.

Allows elements to be introduced into a specification that can't safely be ignored by applications that don't recognize them.

Only the definition of an element can set IsModifier true - either the specification itself or where an extension is originally defined. Once set, it cannot be changed in derived profiles. An element/extension that has isModifier=true SHOULD also have a minimum cardinality of 1, so that there is no lack of clarity about what to do if it is missing. If it can be missing, the definition SHALL make the meaning of a missing element clear.

Whether the element should be included if a client requests a search with the parameter _summary=true.

Allow clients to search through large resources quickly.

Some resources include a set of simple metadata, and some very large data. This element is used to reduce the quantity of data returned in searches. Note that servers may pre-cache summarized resources for optimal performance, so servers might not support per-profile use of the isSummary flag. When a request is made with _summary=true, serailisers only include elements marked as 'isSummary = true'. Other than Attachment.data, all data type properties are included in the summary form. Modifier elements or elements with minimum cardinality = 1 must be marked as summary elements.

Binds to a value set if this element is coded (code, Coding, CodeableConcept, Quantity), or the data types (string, uri).

For a CodeableConcept, when no codes are allowed - only text, use a binding of strength "required" with a description explaining that no coded values are allowed and what sort of information to put in the "text" element.

Indicates the degree of conformance expectations associated with this binding - that is, the degree to which the provided value set must be adhered to in the instances.

For further discussion, see Using Terminologies.

Describes the intended use of this particular set of codes.

Points to the value set or external definition (e.g. implicit value set) that identifies the set of codes to be used. If the binding refers to an explicit value set - the normal case - then use a Reference(ValueSet) preferably containing the canonical URL for the value set. If the reference is to an implicit value set - usually, an IETF RFC that defines a grammar, such as mime types - then use a uri.

For value sets with a referenceResource, the display can contain the value set description. The reference may be version-specific or not.

Identifies a concept from an external specification that roughly corresponds to this element.

Provides guidance to implementers familiar with or converting content from other specifications.

Mappings are not necessarily specific enough for safe translation.

An internal reference to the definition of a mapping.

Identifies the computable language in which mapping.map is expressed.

If omitted, then there can be no expectation of computational interpretation of the mapping.

Expresses what part of the target specification corresponds to this element.

For most mappings, the syntax is undefined. Syntax will be provided for mappings to the RIM. Multiple mappings may be possible and may include constraints on other resource elements that identify when a particular mapping applies.

Comments that provide information about the mapping or its use.