<xs:group name="complexExtensionElementGroup">
    <xs:annotation>
        <xs:documentation> 
        Defines the collection of (sub)elements of an item that are "mappable" as "extension 
        (sub) elements" of an "item/entry" in an existing "standard" content syndication format (RSS/Atom)
        and have "complex" content. 
      </xs:documentation>
    </xs:annotation>
    <xs:sequence>
        <!-- The following elements define a group of "suggested attributes" that are applicable to -->
        <!-- multiple item categories. Note that each of these is merely a suggestion but the user -->
        <!-- is strongly encouraged to use these attributes if they apply to the item they are listing -->
        <xs:element ref="gn:shipping" minOccurs="0" maxOccurs="10" />
    </xs:sequence>
</xs:group>