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3. group

The <group> reference declaration allows you to refer to global element groups within your content model. 

<group ref="global group definition" 
       minOccurs="non negative number" 
       maxOccurs="non negative number or unbounded"> 

This can be done by including a ref attribute and specifying the name of the global <group> declaration: 

<group name="NameGroup"> 
    <sequence> 
        <element name="first" type="string" minOccurs="1" maxOccurs="unbounded"/> 
        <element name="middle" type="string" minOccurs="0" maxOccurs="1"/> 
        <element name="last" type="string"/> 
    </sequence> 
</group> 

<element name="name"> 
    <complexType> 
        <group ref="target:NameGroup"/> 
        <attribute name="title" type="string"/> 
    </complexType> 
</element>