def update_xml(xml, value)
      wrap(xml).tap do |xml|
        value.each_pair do |k, v|
          node = XML.add_node(xml, hash.wrapper)
          @key.update_xml(node, k)
          @value.update_xml(node, v)
        end
      end
    end
def update_xml(xml, value)
      wrap(xml).tap do |xml|
        value.each_pair do |k, v|
          node = XML.add_node(xml, hash.wrapper)
          @key.update_xml(node, k)
          @value.update_xml(node, v)
        end
      end
    end
Updates the composed XML object in the given XML block to
 the value provided.