# File lib/nokogiri/xml/node_set.rb, line 214
      def attr key, value = nil, &blk
        unless Hash === key || key && (value || blk)
          return first.attribute(key)
        end

        hash = key.is_a?(Hash) ? key : { key => value }

        hash.each { |k,v| each { |el| el[k] = v || blk[el] } }

        self
      end