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The Primer states: "Notice that types derived by restriction must repeat all the components of the base type definition that are to be included in the derived type". However, this is not true of attributes. See http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001AprJun/0154.html
An erratum E0-21 was added to the errata document indicating that only particle components need to be repeated.