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* * Complete XML Schema Reference](#) * * * ## Definition and Usage The `attribute` element defines an attribute. ### Element Information * **Parent Elements:** `attributeGroup`, `schema`, `complexType`, `restriction` (both `simpleContent` and `complexContent`), `extension` (both `simpleContent` and `complexContent`) ### Syntax (annotation?,(simpleType?)) (The ? symbol indicates that the element can occur zero or one time within the `attribute` element.) | Attribute | Description | | --- | --- | | default | Optional. Specifies the default value for the attribute. The `default` and `fixed` attributes cannot both be present. | | fixed | Optional. Specifies a fixed value for the attribute. The `default` and `fixed` attributes cannot both be present. | | form | Optional. Specifies the form of the attribute. The default value is the value of the `attributeFormDefault` attribute of the `schema` element containing this attribute. Can be set to one of the following values: * "qualified" - Indicates that this attribute must be qualified with a namespace prefix and its NCName (No-Colon Name). * "unqualified" - Indicates that this attribute does not need to be qualified with a namespace prefix and does not need to match its NCName (i.e., local name). | | id | Optional. Specifies a unique ID for this element. | | name | Optional. Specifies the name of the attribute. The `name` and `ref` attributes cannot both be present. | | ref | Optional. Specifies a reference to a specified attribute. The `name` and `ref` attributes cannot both be present. If `ref` appears, the `simpleType` element, `form`, and `type` cannot appear. | | type | Optional. Specifies a built-in data type or a simple type. The `type` attribute can only appear when the content does not contain a `simpleType` element. | | use | Optional. Specifies how the attribute is used. Can be set to one of the following values: * optional - The attribute is optional and can have any value (default). * prohibited - The attribute cannot be used. * required - The attribute is required. | | _any attributes_ | Optional. Specifies any other attributes with a non-schema namespace. | ### Example 1 The example above indicates that the "code" attribute has a constraint. The only acceptable values are two uppercase letters from A to Z. ### Example 2 To declare an attribute using an existing attribute definition within a complex type, use the `ref` attribute: ### Example 3 An attribute can have either a default value or a specified fixed value. If no other value is specified, the default value is automatically assigned to the attribute. In the example below, the default value is "EN": If no other value is specified, the fixed value is automatically assigned to the attribute. However, unlike the default value, if you specify a value other than the fixed value for the attribute, the document will be validated as invalid. In the example below, the fixed value is "EN": ### Example 4 All attributes are optional by default. To explicitly specify an attribute as optional, use the "use" attribute: To make an attribute required: * * Complete XML Schema Reference](#)