/*
 * call-seq:
 *  root=
 *
 * Set the root element on this document
 */
static VALUE set_root(VALUE self, VALUE root)
{
  xmlDocPtr doc;
  xmlNodePtr new_root;
  xmlNodePtr old_root;

  Data_Get_Struct(self, xmlDoc, doc);

  old_root = NULL;

  if(NIL_P(root)) {
    old_root = xmlDocGetRootElement(doc);

    if(old_root) {
      xmlUnlinkNode(old_root);
      NOKOGIRI_ROOT_NODE(old_root);
    }

    return root;
  }

  Data_Get_Struct(root, xmlNode, new_root);


  /* If the new root's document is not the same as the current document,
   * then we need to dup the node in to this document. */
  if(new_root->doc != doc) {
    old_root = xmlDocGetRootElement(doc);
    if (!(new_root = xmlDocCopyNode(new_root, doc, 1))) {
      rb_raise(rb_eRuntimeError, "Could not reparent node (xmlDocCopyNode)");
    }
  }

  xmlDocSetRootElement(doc, new_root);
  if(old_root) NOKOGIRI_ROOT_NODE(old_root);
  return root;
}