instance_controller with multiple skeleton's

Hi,

I don’t grasp the concept of a instance_controller having multiple skeleton elements:

<instance_controller>
  <skeleton>Bone_1</skeleton>
  <skeleton>Bone_2</skeleton>
   ...

Can someone explain the concept? Don’t understand how to traverse the visual_scene’s <node>'s to create the final skeleton.

Thanks a lot!
Tim Knip