    # File lib/nokogiri/xml/node_set.rb, line 163
          def attr key, value = nil, &blk
            if value or blk
              each do |el|
                el.set_attribute(key, value || blk[el])
              end
              return self
            end
            if key.is_a? Hash
              key.each { |k,v| self.attr(k,v) }
              return self
            else
              return self[0].get_attribute(key)
            end
          end