You use an xs:group element to define a model group.

You give it a name that you can then refer to using a QName.

The content is just like xs:complexType in that it must start with xs:all, xs:sequence, or xs:choice.

A declaration:

<xs:group name="ListContents">
<xs:sequence>
<xs:element name="item" maxOccurs="unbounded"/>
</xs:sequence>
</xs:group>

A reference:

<xs:group ref="my:ListContents"/>