CarGroup 

Train carriages (ay want to change name later into
carriage

Element Group Information

Model

Car | Cars
Children: Car, Cars

Used By

Element Cars
Complex Type TrainType

Source 

<xs:group name="CarGroup">
  <xs:annotation>
    <xs:documentation>Train carriages (ay want to change name later into carriage</xs:documentation>
  </xs:annotation>
  <xs:choice>
    <xs:annotation>
      <xs:documentation>One or many</xs:documentation>
    </xs:annotation>
    <xs:element ref="Car"/>
    <xs:element ref="Cars"/>
  </xs:choice>
</xs:group>