XML Schema Complete Reference, The

11.9. The extension Element

The extension element applies to complex types that contain simple content as well as complex types that contain complex content. The extension element provides functionality for adding attribute types to simple content. For complex content, the extension element provides functionality for adding either attributes or nested element types. Finally, with respect to simple content, the base type can be either a simple type or a complex type that contains simple content.

Tip

The use of the final attribute on the base complex type may prohibit the extension of that complex type. In addition, the use of a fixed attribute on a constraining facet of the base complex type may prohibit further modification of that constraining ...