Specifies whether the topic or map referenced should be processed normally or treated as a resource that is only included in order to resolve key or content references.

processing-role="normal"
  The topic is a readable part of the information set. It is included in navigation and search results. This is the default value for the <topicref> element.
processing-role="resource-only"
  The topic should be used only as a resource for processing. It is not included in navigation or search results, nor is it rendered as a topic. This is the default value for the <keydef> element.

If the @processing-role attribute is not specified locally, the value cascades from the closest element in the containment hierarchy.