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# XML Schema extension Element * * Complete XML Schema Reference Manual](#) * * * ## Definition and Usage The extension element extends a simpleType or complexType element. ### Element Information * **Parent elements:** simpleContent, complexContent ### Syntax (annotation?,((group|all|choice|sequence)?, ((attribute|attributeGroup)*,anyAttribute?))) (? indicates that the element may appear zero or one time within the extension element; * indicates that the element may appear zero or more times.) | Attribute | Description | | --- | --- | | id | Optional. Specifies a unique ID for the element. | | base | Required. Specifies the name of a built-in data type, simpleType, or complexType element. | | xml:lang | Optional. Specifies the language used in the content. | ### Example 1 The following example extends an existing simpleType by adding attributes: <xs:simple