15.2.43. XML Schema key element

Definition and usage ¶

The key element specifies that an attribute or element value (or set of values) must be a key within the specified range. The scope of the key is the containing element in the instance document. The key means that the data should be unique, non-zero, and always exist within the specified range.

The key element must contain the following elements in order:

The selector element contains an XPath expression that specifies a set of elements in which the value specified by field must be unique.

Element information ¶

父元素： Element

Grammar ¶

<key
id=ID
name=NCName
*any attributes*
>
(annotation?,(selector,field+))
</key>

(? The symbol declares that in the key element, the element can appear zero or once, and the + symbol declares that the element must appear one or more times. )

Attribute	Description
Id	Optional. Specifies the unique ID of the element.
Name	Necessary. Specifies the name of the key element.
Any attributes	Optional. Specifies any other attributes with the non-schema namespace.

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