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.

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.

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.

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 resource SHALL conform to at least one profile defined in the implementation guide.

Identifies a profile structure or implementation Guide that SHALL hold 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 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 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.

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

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.

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 may 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 may 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.

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.

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.