P5: Guidelines for Electronic Text Encoding and Interchange

<rng:element name="relatedItem">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.typed.attributes"/>
 <rng:choice>
  <rng:ref name="model.biblLike"/>
  <rng:ref name="model.ptrLike"/>
 </rng:choice>
</rng:element>

element relatedItem
{
   att.global.attributes,
   att.typed.attributes,
   ( model.biblLike | model.ptrLike )
}