XML Schema selector 元素
定义和用法
selector 元素指定 XML 路径语言 (XPath) 表达式，该表达式为标识约束选择一组元素（unique、key 和 keyref 元素）。
Element information
| Appearance times | Once |
| Parent element | key, keyref, unique |
| Content | annotation |
Grammar
<selector id=ID xpath=a subset of XPath expression any attributes > (annotation?) </selector>
| Attribute | Description |
|---|---|
| id | Optional. Specifies the unique ID of the element. |
| xpath | Required. Specifies the XPath expression relative to the declared element. This expression identifies the child elements that apply the identified constraint (the declared element). |
| any attributes | Optional. Specifies any other attributes with non-schema namespace. |
