< Complete XML Schema Reference
Definition and Usage
The key element specifies an attribute or element value as a key (unique, non-nullable, and always present) within the containing element in an instance document.
The key 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
<key
id=ID
name=NCName
any attributes
>
(annotation?,(selector,field+))
</key>
(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 key element)
| Attribute | Description |
|---|---|
| id | Optional. Specifies a unique ID for the element |
| name | Required. Specifies the name of the key element |
| any attributes | Optional. Specifies any other attributes with non-schema namespace |
< Complete XML Schema Reference