---
type: "datatype"
title: "BackboneElement"
datatype: "BackboneElement"
source: "source/types.html#BackboneElement"
---
# BackboneElement

- [Type Framework](/types#BackboneElement)
- [Definitions](/types-definitions#BackboneElement)
- [Mappings](/types-mappings#BackboneElement)
- [Profiles](/types-profiles#BackboneElement)

## Overview

See also [Detailed Descriptions](types-definitions#BackboneElement), [Mappings](types-mappings#BackboneElement), [Profiles](types-profiles#BackboneElement) and [Extensions]([%extensions-location%]extensions-types#BackboneElement)

The base definition for complex elements defined as part of a resource definition - that is, elements that have children that are defined in the resource. [Datatype](datatypes) elements do not use this type. For instance, [Patient.contact](patient#resource) is an element that is defined as part of the patient resource, so it automatically has the type `BackboneElement`.

Note that the descendant types of `BackboneElement` are all declared implicitly as part of the definitions of the resources.

\[%adt BackboneElement 1%\]

## Elements

- **[BackboneElement.modifierExtension](/types-definitions#BackboneElement.modifierExtension)** [0..*]: [Extension](/Extension) 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)

## Aliases

- **BackboneElement.modifierExtension**: extensions, user content, modifiers

## Modifiers

- **BackboneElement.modifierExtension**: Is modifier

## Summary Elements

- **BackboneElement.modifierExtension**: In _summary view

## Requirements

- **BackboneElement.modifierExtension**: 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](extensibility.html#modifierExtension)

## Comments

- **BackboneElement.modifierExtension**: 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

## Mappings

- **BackboneElement.modifierExtension**: RIM Mapping: N/A