Represents a defined collection of entities that may be discussed or acted upon collectively but which are not expected to act collectively, and are not formally or legally recognized; i.e. a collection of entities that isn't an Organization.

If both Group.characteristic and Group.member are present, then the members are the individuals who were found who met the characteristic. It's possible that there might be other candidate members who meet the characteristic and aren't (yet) in the list. All members SHALL have the listed characteristics.

A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of its narrative along with other profiles, value sets, etc.

These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, nor can they have their own independent transaction scope. This is allowed to be a Parameters resource if and only if it is referenced by a resource that provides context/meaning.

This should never be done when the content can be identified properly, as once identification is lost, it is extremely difficult (and context dependent) to restore it again. Contained resources may have profiles and tags in their meta elements, but SHALL NOT have security labels.

An absolute URI that is used to identify this artifact when it is referenced in a specification, model, design or an instance; also called its canonical identifier. This SHOULD be globally unique and SHOULD be a literal address at which an authoritative instance of this artifact is (or will be) published. This URL can be the target of a canonical reference. It SHALL remain the same when the artifact is stored on different servers.

Can be a urn:uuid: or a urn:oid: but real http: addresses are preferred. Multiple instances may share the same URL if they have a distinct version.

The determination of when to create a new version of a resource (same url, new version) vs. defining a new artifact is up to the author. Considerations for making this decision are found in Technical and Business Versions.

In some cases, the resource can no longer be found at the stated url, but the url itself cannot change. Implementations can use the meta.source element to indicate where the current master source of the resource can be found.

The identifier that is used to identify this version of the artifact when it is referenced in a specification, model, design or instance. This is an arbitrary value managed by the artifact author and is not expected to be globally unique. For example, it might be a timestamp (e.g. yyyymmdd) if a managed version is not available. There is also no expectation that versions can be placed in a lexicographical sequence.

Indicates the mechanism used to compare versions to determine which is more current.

If set as a string, this is a FHIRPath expression that has two additional context variables passed in - %version1 and %version2 and will return a negative number if version1 is newer, a positive number if version2 and a 0 if the version ordering can't be successfully be determined.

A short, descriptive, user-friendly title for the artifact.

This name does not need to be machine-processing friendly and may contain punctuation, white-space, etc.

A Boolean value to indicate that this artifact is authored for testing purposes (or education/evaluation/marketing) and is not intended to be used for genuine usage.

The date (and optionally time) when the artifact was last significantly changed. The date must change when the business version changes and it must change if the status code changes. In addition, it should change when the substantive content of the artifact changes.

The date is often not tracked until the resource is published, but may be present on draft content. Note that this is not the same as the resource last-modified-date, since the resource may be a secondary representation of the artifact. Additional specific dates may be added as extensions or be found by consulting Provenances associated with past versions of the resource.

The name of the organization or individual responsible for the release and ongoing maintenance of the artifact.

Usually an organization but may be an individual. The publisher (or steward) of the artifact is the organization or individual primarily responsible for the maintenance and upkeep of the artifact. This is not necessarily the same individual or organization that developed and initially authored the content. The publisher is the primary point of contact for questions or issues with the artifact. This item SHOULD be populated unless the information is available from context.

Contact details to assist a user in finding and communicating with the publisher.

May be a web site, an email address, a telephone number, etc.

The content was developed with a focus and intent of supporting the contexts that are listed. These contexts may be general categories (gender, age, ...) or may be references to specific programs (insurance plans, studies, ...) and may be used to assist with indexing and searching for appropriate artifact instances.

When multiple useContexts are specified, there is no expectation that all or any of the contexts apply.

Explanation of why this artifact is needed and why it has been designed as it has.

This element does not describe the usage of the artifact. Instead, it provides traceability of ''why'' the resource is either needed or ''why'' it is defined as it is. This may be used to point to source materials or specifications that drove the structure of this artifact.

A copyright statement relating to the artifact and/or its contents. Copyright statements are generally legal restrictions on the use and publishing of the artifact.

The short copyright declaration (e.g. (c) '2015+ xyz organization' should be sent in the copyrightLabel element.

A short string (<50 characters), suitable for inclusion in a page footer that identifies the copyright holder, effective period, and optionally whether rights are resctricted. (e.g. 'All rights reserved', 'Some rights reserved').

Defines the content expected to be rendered in all representations of the artifact. The (c) symbol should NOT be included in this string. It is expected to be added by software when rendering the notation. Full details about licensing, restrictions, warrantees, etc. goes in the more general 'copyright' element.

An individual or organization primarily involved in the creation and maintenance of the artifact.

Related artifacts such as additional documentation, justification, dependencies, bibliographic references, and predecessor and successor artifacts.

Each related artifact is either an attachment, or a reference to another resource, but not both.

An expression that defines the criteria for group membership. This extension can only be used on a Group resource with a membership of definitional. When this expression is used, the Group resource cannot have any characteristic elements; this mechanism is exclusive with characteristics. The result of the expression SHALL be boolean-valued. The expression SHALL be parameterized with a %context variable that represents the subject being tested for membership. If evaluation of the expression results in true, the subject is considered a member of the group.

Used to specify how two or more characteristics are combined.

Provides the value of n when at-least or at-most codes are used for combinationMethod.

An Extension

The status of this artifact. Enables tracking the life-cycle of the content.

Indicates whether the record for the group is available for use or is merely being retained for historical purposes.

Need to be able to mark a group record as not to be used because it was created in error or is otherwise no longer available (e.g. a herd that no longer exists).

Identifies the broad classification of the kind of resources the group includes.

Group members SHALL be of the appropriate resource type (Patient for person or animal; or Practitioner, PractitionerRole, Device, CareTeam, HealthcareService, Location, Organization, RelatedPerson, or Specimen for the other types.), or a Group of the resources of the appropriate type.

Types of resources that are part of group.

Identifies what type of resources the group is made up of.

Basis for membership in the Group:

• 'definitional': The Group.characteristics specified are both necessary and sufficient to determine membership. All entities that meet the criteria are considered to be members of the group, whether referenced by the group or not. If members are present, they are individuals that happen to be known as meeting the Group.characteristics. The list cannot be presumed to be complete.
• 'enumerated': The Group.characteristics are necessary but not sufficient to determine membership. Membership is determined by being listed as one of the Group.member.

The basis for membership in a group

There are use-cases for groups that define specific collections of individuals, and other groups that define "types" of intended individuals. The requirements for both kinds of groups are similar, so we use a single resource, distinguished by this element.

Identifies traits whose presence r absence is shared by members of the group.

All the identified characteristics must be true for an entity to a member of the group.

Needs to be a generic mechanism for identifying what individuals can be part of a group.

The value of the trait that holds for members of the group, held by uri.

The value of the trait that holds for members of the group, held by Expression.

A short, natural language description of the characteristic that could be used to communicate the criteria to an end-user.

Method for how the characteristic value was determined.

Method for how the characteristic value was determined.

Method for how the characteristic value was determined.

Defines the reference point for comparison when other than 0.

Number of occurrences meeting the characteristic.

Number of occurrences meeting the characteristic.

Length of time in which the characteristic is met.

Length of time in which the characteristic is met.

Timing in which the characteristic is determined.

May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

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.

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

A code that identifies the kind of trait being asserted.

List of characteristics used to describe group members; e.g. gender, age, owner, location, etc.

Need a formal way of identifying the characteristic being described.

A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

Very often the text is the same as a displayName of one of the codings.

The codes from the terminologies do not always capture the correct meaning with all the nuances of the human using them, or sometimes there is no appropriate code at all. In these cases, the text is used to capture the full meaning of the source.

The value of the trait that holds (or does not hold - see 'exclude') for members of the group.

For Range, it means members of the group have a value that falls somewhere within the specified range.

Value of descriptive member characteristic; e.g. red, male, pneumonia, Caucasian, etc.

The value of the characteristic is what determines group membership.

The value of the trait that holds (or does not hold - see 'exclude') for members of the group.

For Range, it means members of the group have a value that falls somewhere within the specified range.

The value of the characteristic is what determines group membership.

If true, indicates the characteristic is one that is NOT held by members of the group.

This is labeled as "Is Modifier" because applications cannot wrongly include excluded members as included or vice versa.

Sometimes group membership is determined by characteristics not possessed.

Represents a defined collection of entities that may be discussed or acted upon collectively but which are not expected to act collectively, and are not formally or legally recognized; i.e. a collection of entities that isn't an Organization.

If both Group.characteristic and Group.member are present, then the members are the individuals who were found who met the characteristic. It's possible that there might be other candidate members who meet the characteristic and aren't (yet) in the list. All members SHALL have the listed characteristics.

The logical id of the resource, as used in the URL for the resource. Once assigned, this value never changes.

Within the context of the FHIR RESTful interactions, the resource has an id except for cases like the create and conditional update. Otherwise, the use of the resouce id depends on the given use case.

The metadata about the resource. This is content that is maintained by the infrastructure. Changes to the content might not always be associated with version changes to the resource.

A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of its narrative along with other profiles, value sets, etc.

The base language in which the resource is written.

Language is provided to support indexing and accessibility (typically, services such as text to speech use the language tag). The html language tag in the narrative applies to the narrative. The language tag on the resource may be used to specify the language of other presentations generated from the data in the resource. Not all the content has to be in the base language. The Resource.language should not be assumed to apply to the narrative automatically. If a language is specified, it should it also be specified on the div element in the html (see rules in HTML5 for information about the relationship between xml:lang and the html lang attribute).

IETF language tag for a human language

A human-readable narrative that contains a summary of the resource and can be used to represent the content of the resource to a human. The narrative need not encode all the structured data, but is required to contain sufficient detail to make it "clinically safe" for a human to just read the narrative. Resource definitions may define what content should be represented in the narrative to ensure clinical safety.

Contained resources do not have a narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded information is added later.

These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, nor can they have their own independent transaction scope. This is allowed to be a Parameters resource if and only if it is referenced by a resource that provides context/meaning.

This should never be done when the content can be identified properly, as once identification is lost, it is extremely difficult (and context dependent) to restore it again. Contained resources may have profiles and tags in their meta elements, but SHALL NOT have security labels.

An Extension

An absolute URI that is used to identify this artifact when it is referenced in a specification, model, design or an instance; also called its canonical identifier. This SHOULD be globally unique and SHOULD be a literal address at which an authoritative instance of this artifact is (or will be) published. This URL can be the target of a canonical reference. It SHALL remain the same when the artifact is stored on different servers.

Can be a urn:uuid: or a urn:oid: but real http: addresses are preferred. Multiple instances may share the same URL if they have a distinct version.

The determination of when to create a new version of a resource (same url, new version) vs. defining a new artifact is up to the author. Considerations for making this decision are found in Technical and Business Versions.

In some cases, the resource can no longer be found at the stated url, but the url itself cannot change. Implementations can use the meta.source element to indicate where the current master source of the resource can be found.

The identifier that is used to identify this version of the artifact when it is referenced in a specification, model, design or instance. This is an arbitrary value managed by the artifact author and is not expected to be globally unique. For example, it might be a timestamp (e.g. yyyymmdd) if a managed version is not available. There is also no expectation that versions can be placed in a lexicographical sequence.

Indicates the mechanism used to compare versions to determine which is more current.

If set as a string, this is a FHIRPath expression that has two additional context variables passed in - %version1 and %version2 and will return a negative number if version1 is newer, a positive number if version2 and a 0 if the version ordering can't be successfully be determined.

A short, descriptive, user-friendly title for the artifact.

This name does not need to be machine-processing friendly and may contain punctuation, white-space, etc.

A Boolean value to indicate that this artifact is authored for testing purposes (or education/evaluation/marketing) and is not intended to be used for genuine usage.

The date (and optionally time) when the artifact was last significantly changed. The date must change when the business version changes and it must change if the status code changes. In addition, it should change when the substantive content of the artifact changes.

The date is often not tracked until the resource is published, but may be present on draft content. Note that this is not the same as the resource last-modified-date, since the resource may be a secondary representation of the artifact. Additional specific dates may be added as extensions or be found by consulting Provenances associated with past versions of the resource.

The name of the organization or individual responsible for the release and ongoing maintenance of the artifact.

Usually an organization but may be an individual. The publisher (or steward) of the artifact is the organization or individual primarily responsible for the maintenance and upkeep of the artifact. This is not necessarily the same individual or organization that developed and initially authored the content. The publisher is the primary point of contact for questions or issues with the artifact. This item SHOULD be populated unless the information is available from context.

Contact details to assist a user in finding and communicating with the publisher.

May be a web site, an email address, a telephone number, etc.

The content was developed with a focus and intent of supporting the contexts that are listed. These contexts may be general categories (gender, age, ...) or may be references to specific programs (insurance plans, studies, ...) and may be used to assist with indexing and searching for appropriate artifact instances.

When multiple useContexts are specified, there is no expectation that all or any of the contexts apply.

Explanation of why this artifact is needed and why it has been designed as it has.

This element does not describe the usage of the artifact. Instead, it provides traceability of ''why'' the resource is either needed or ''why'' it is defined as it is. This may be used to point to source materials or specifications that drove the structure of this artifact.

A copyright statement relating to the artifact and/or its contents. Copyright statements are generally legal restrictions on the use and publishing of the artifact.

The short copyright declaration (e.g. (c) '2015+ xyz organization' should be sent in the copyrightLabel element.

A short string (<50 characters), suitable for inclusion in a page footer that identifies the copyright holder, effective period, and optionally whether rights are resctricted. (e.g. 'All rights reserved', 'Some rights reserved').

Defines the content expected to be rendered in all representations of the artifact. The (c) symbol should NOT be included in this string. It is expected to be added by software when rendering the notation. Full details about licensing, restrictions, warrantees, etc. goes in the more general 'copyright' element.

An individual or organization primarily involved in the creation and maintenance of the artifact.

Related artifacts such as additional documentation, justification, dependencies, bibliographic references, and predecessor and successor artifacts.

Each related artifact is either an attachment, or a reference to another resource, but not both.

An expression that defines the criteria for group membership. This extension can only be used on a Group resource with a membership of definitional. When this expression is used, the Group resource cannot have any characteristic elements; this mechanism is exclusive with characteristics. The result of the expression SHALL be boolean-valued. The expression SHALL be parameterized with a %context variable that represents the subject being tested for membership. If evaluation of the expression results in true, the subject is considered a member of the group.

Used to specify how two or more characteristics are combined.

Provides the value of n when at-least or at-most codes are used for combinationMethod.

An Extension

The status of this artifact. Enables tracking the life-cycle of the content.

Business identifiers assigned to this participant by one of the applications involved. These identifiers remain constant as the resource is updated and propagates from server to server.

Note: This is a business identifier, not a resource identifier (see discussion). It is best practice for the identifier to only appear on a single resource instance, however business practices may occasionally dictate that multiple resource instances with the same identifier can exist - possibly even with different resource types.

Allows identification of the group as it is known by various participating systems and in a way that remains consistent across servers.

Indicates whether the record for the group is available for use or is merely being retained for historical purposes.

Need to be able to mark a group record as not to be used because it was created in error or is otherwise no longer available (e.g. a herd that no longer exists).

Identifies the broad classification of the kind of resources the group includes.

Group members SHALL be of the appropriate resource type (Patient for person or animal; or Practitioner, PractitionerRole, Device, CareTeam, HealthcareService, Location, Organization, RelatedPerson, or Specimen for the other types.), or a Group of the resources of the appropriate type.

Types of resources that are part of group.

Identifies what type of resources the group is made up of.

Basis for membership in the Group:

• 'definitional': The Group.characteristics specified are both necessary and sufficient to determine membership. All entities that meet the criteria are considered to be members of the group, whether referenced by the group or not. If members are present, they are individuals that happen to be known as meeting the Group.characteristics. The list cannot be presumed to be complete.
• 'enumerated': The Group.characteristics are necessary but not sufficient to determine membership. Membership is determined by being listed as one of the Group.member.

The basis for membership in a group

There are use-cases for groups that define specific collections of individuals, and other groups that define "types" of intended individuals. The requirements for both kinds of groups are similar, so we use a single resource, distinguished by this element.

Provides a specific type of resource the group includes; e.g. "cow", "syringe", etc.

This would generally be omitted for Person resources.

Kind of particular resource; e.g. cow, syringe, lake, etc.

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

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.

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.

A reference to a code defined by a terminology system.

Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

Allows for alternative encodings within a code system, and translations to other code systems.

A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

Very often the text is the same as a displayName of one of the codings.

The codes from the terminologies do not always capture the correct meaning with all the nuances of the human using them, or sometimes there is no appropriate code at all. In these cases, the text is used to capture the full meaning of the source.

A label assigned to the group for human identification and communication.

Used to identify the group in human communication.

Explanation of what the group represents and how it is intended to be used.

A count of the number of resource instances that are part of the group.

Note that the quantity may be less than the number of members if some of the members are not active.

Group size is a common defining characteristic.

Entity responsible for defining and maintaining Group characteristics and/or registered members.

This does not strictly align with ownership of a herd or flock, but may suffice to represent that relationship in simple cases. More complex cases will require an extension.

Identifies traits whose presence r absence is shared by members of the group.

All the identified characteristics must be true for an entity to a member of the group.

Needs to be a generic mechanism for identifying what individuals can be part of a group.

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

An Extension

The value of the trait that holds for members of the group, held by uri.

The value of the trait that holds for members of the group, held by Expression.

A short, natural language description of the characteristic that could be used to communicate the criteria to an end-user.

Method for how the characteristic value was determined.

Method for how the characteristic value was determined.

Method for how the characteristic value was determined.

Defines the reference point for comparison when other than 0.

Number of occurrences meeting the characteristic.

Number of occurrences meeting the characteristic.

Length of time in which the characteristic is met.

Length of time in which the characteristic is met.

Timing in which the characteristic is determined.

May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

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.

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

A code that identifies the kind of trait being asserted.

List of characteristics used to describe group members; e.g. gender, age, owner, location, etc.

Need a formal way of identifying the characteristic being described.

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

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.

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.

A reference to a code defined by a terminology system.

Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

Allows for alternative encodings within a code system, and translations to other code systems.

A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

Very often the text is the same as a displayName of one of the codings.

The codes from the terminologies do not always capture the correct meaning with all the nuances of the human using them, or sometimes there is no appropriate code at all. In these cases, the text is used to capture the full meaning of the source.

The value of the trait that holds (or does not hold - see 'exclude') for members of the group.

For Range, it means members of the group have a value that falls somewhere within the specified range.

Value of descriptive member characteristic; e.g. red, male, pneumonia, Caucasian, etc.

The value of the characteristic is what determines group membership.

The value of the trait that holds (or does not hold - see 'exclude') for members of the group.

For Range, it means members of the group have a value that falls somewhere within the specified range.

The value of the characteristic is what determines group membership.

If true, indicates the characteristic is one that is NOT held by members of the group.

This is labeled as "Is Modifier" because applications cannot wrongly include excluded members as included or vice versa.

Sometimes group membership is determined by characteristics not possessed.

The period over which the characteristic is tested; e.g. the patient had an operation during the month of June.

Identifies the resource instances that are members of the group.

Often the only thing of interest about a group is "who's in it".

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

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.

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.

May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

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.

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

A reference to the entity that is a member of the group. Must be consistent with Group.type. If the entity is another group, then the type must be the same.

The period that the member was in the group, if known.

Need to track who was in a group at a particular time.

A flag to indicate that the member is no longer in the group, but previously may have been a member.

Sometimes you don't know when someone stopped being in a group, but not when.