# File lib/xml/dom/core.rb, line 703
      def __sibling(reverse, only_appeared_before_self)
        return if @parent.nil?
        self_appeared = false
        @parent.childNodes.reversible_each(reverse) do |node|
          if node == self
            self_appeared = true
            next
          end
          if only_appeared_before_self
            break if self_appeared
            yield node
          else # only appeared after self
            yield node if self_appeared
          end
        end
      end