# XML Schema keyref Element

Complete XML Schema Reference

## Definition and Usage

The keyref element specifies that an attribute or element value correspond to those of the specified key or unique element.

The keyref element MUST contain the following (in order):

- one and only one selector element (contains an XPath expression that specifies the set of elements across which the values specified by field must be unique)
- one or more field elements (contains an XPath expression that specifies the values that must be unique for the set of elements specified by the selector element)

### Element Information

- Parent elements: element

### Syntax

<keyref
id=ID
name=NCName
refer=QName
any attributes
>
(annotation?,(selector,field+))
</keyref>

(The ? sign declares that the element can occur zero or one time, and the + sign declares that the element must occur one or more times inside the keyref element)

Attribute | Description
--- | ---
id | Optional. Specifies a unique ID for the element
name | Required. Specifies the name of the keyref element
refer | Required. Specifies the name of a key or unique element defined in this or another schema
any attributes | Optional. Specifies any other attributes with non-schema namespace

Complete XML Schema Reference

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