def forget_tree(element_id, view)
      removed = forget_view(element_id, view)
      if view.subviews
        view.subviews.each do | sub |
          if (sub_ids = sub.motion_kit_meta[:motion_kit_ids])
            sub_ids.each do | sub_id |
              forget_tree(sub_id, sub) || []
            end
          end
        end
      end
      removed
    end
def forget_tree(element_id, view)
      removed = forget_view(element_id, view)
      if view.subviews
        view.subviews.each do | sub |
          if (sub_ids = sub.motion_kit_meta[:motion_kit_ids])
            sub_ids.each do | sub_id |
              forget_tree(sub_id, sub) || []
            end
          end
        end
      end
      removed
    end
returns the root view that was removed, if any