Raised if <code>offset</code> is negative or greater 
   than the number of child units in <code>refNode</code>. Child units 
   are 16-bit units if <code>refNode</code> is a type of CharacterData 
   node (e.g., a Text or Comment node) or a ProcessingInstruction 
   node. Child units are Nodes in all other cases.
   <br>INVALID_STATE_ERR: Raised if <code>detach()</code> has already 
   been invoked on this object.
   <br>WRONG_DOCUMENT_ERR: Raised if <code>refNode</code> was created 
   from a different do