# File lib/mail/parsers/rfc2822.rb, line 3986
    def _nt_zone
      start_index = index
      if node_cache[:zone].has_key?(index)
        cached = node_cache[:zone][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0 = index
      i1, s1 = index, []
      i2 = index
      if has_terminal?("+", false, index)
        r3 = instantiate_node(SyntaxNode,input, index...(index + 1))
        @index += 1
      else
        terminal_parse_failure("+")
        r3 = nil
      end
      if r3
        r2 = r3
      else
        if has_terminal?("-", false, index)
          r4 = instantiate_node(SyntaxNode,input, index...(index + 1))
          @index += 1
        else
          terminal_parse_failure("-")
          r4 = nil
        end
        if r4
          r2 = r4
        else
          @index = i2
          r2 = nil
        end
      end
      s1 << r2
      if r2
        r5 = _nt_DIGIT
        s1 << r5
        if r5
          r6 = _nt_DIGIT
          s1 << r6
          if r6
            r7 = _nt_DIGIT
            s1 << r7
            if r7
              r8 = _nt_DIGIT
              s1 << r8
            end
          end
        end
      end
      if s1.last
        r1 = instantiate_node(SyntaxNode,input, i1...index, s1)
        r1.extend(Zone0)
      else
        @index = i1
        r1 = nil
      end
      if r1
        r0 = r1
      else
        r9 = _nt_obs_zone
        if r9
          r0 = r9
        else
          @index = i0
          r0 = nil
        end
      end

      node_cache[:zone][start_index] = r0

      r0
    end