# File lib/mail/parsers/content_type.rb, line 801
    def _nt_parameter
      start_index = index
      if node_cache[:parameter].has_key?(index)
        cached = node_cache[:parameter][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0, s0 = index, []
      r2 = _nt_CFWS
      if r2
        r1 = r2
      else
        r1 = instantiate_node(SyntaxNode,input, index...index)
      end
      s0 << r1
      if r1
        r3 = _nt_attribute
        s0 << r3
        if r3
          if has_terminal?("=", false, index)
            r4 = instantiate_node(SyntaxNode,input, index...(index + 1))
            @index += 1
          else
            terminal_parse_failure("=")
            r4 = nil
          end
          s0 << r4
          if r4
            r5 = _nt_value
            s0 << r5
            if r5
              r7 = _nt_CFWS
              if r7
                r6 = r7
              else
                r6 = instantiate_node(SyntaxNode,input, index...index)
              end
              s0 << r6
            end
          end
        end
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(Parameter0)
        r0.extend(Parameter1)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:parameter][start_index] = r0

      r0
    end