# File lib/xtemplate/xpath.rb, line 135
      def rename(val, x, y)
        case val
        when Hash
          newval = val.dup
          if( v = newval[x] )
            newval[y] = v
            newval.delete(x)
          end
          newval
        when Array
          val.collect{|v| rename(v, x, y)}
        else
          nil
        end
      end