# File lib/mail/parsers/rfc2822_obsolete.rb, line 962
    def _nt_obs_zone
      start_index = index
      if node_cache[:obs_zone].has_key?(index)
        cached = node_cache[:obs_zone][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0 = index
      if has_terminal?("UT", false, index)
        r1 = instantiate_node(SyntaxNode,input, index...(index + 2))
        @index += 2
      else
        terminal_parse_failure("UT")
        r1 = nil
      end
      if r1
        r0 = r1
      else
        if has_terminal?("GMT", false, index)
          r2 = instantiate_node(SyntaxNode,input, index...(index + 3))
          @index += 3
        else
          terminal_parse_failure("GMT")
          r2 = nil
        end
        if r2
          r0 = r2
        else
          if has_terminal?("EST", false, index)
            r3 = instantiate_node(SyntaxNode,input, index...(index + 3))
            @index += 3
          else
            terminal_parse_failure("EST")
            r3 = nil
          end
          if r3
            r0 = r3
          else
            if has_terminal?("EDT", false, index)
              r4 = instantiate_node(SyntaxNode,input, index...(index + 3))
              @index += 3
            else
              terminal_parse_failure("EDT")
              r4 = nil
            end
            if r4
              r0 = r4
            else
              if has_terminal?("CST", false, index)
                r5 = instantiate_node(SyntaxNode,input, index...(index + 3))
                @index += 3
              else
                terminal_parse_failure("CST")
                r5 = nil
              end
              if r5
                r0 = r5
              else
                if has_terminal?("CDT", false, index)
                  r6 = instantiate_node(SyntaxNode,input, index...(index + 3))
                  @index += 3
                else
                  terminal_parse_failure("CDT")
                  r6 = nil
                end
                if r6
                  r0 = r6
                else
                  if has_terminal?("MST", false, index)
                    r7 = instantiate_node(SyntaxNode,input, index...(index + 3))
                    @index += 3
                  else
                    terminal_parse_failure("MST")
                    r7 = nil
                  end
                  if r7
                    r0 = r7
                  else
                    if has_terminal?("MDT", false, index)
                      r8 = instantiate_node(SyntaxNode,input, index...(index + 3))
                      @index += 3
                    else
                      terminal_parse_failure("MDT")
                      r8 = nil
                    end
                    if r8
                      r0 = r8
                    else
                      if has_terminal?("PST", false, index)
                        r9 = instantiate_node(SyntaxNode,input, index...(index + 3))
                        @index += 3
                      else
                        terminal_parse_failure("PST")
                        r9 = nil
                      end
                      if r9
                        r0 = r9
                      else
                        if has_terminal?("PDT", false, index)
                          r10 = instantiate_node(SyntaxNode,input, index...(index + 3))
                          @index += 3
                        else
                          terminal_parse_failure("PDT")
                          r10 = nil
                        end
                        if r10
                          r0 = r10
                        else
                          if has_terminal?('\G[\\x41-\\x49]', true, index)
                            r11 = true
                            @index += 1
                          else
                            r11 = nil
                          end
                          if r11
                            r0 = r11
                          else
                            if has_terminal?('\G[\\x4B-\\x5A]', true, index)
                              r12 = true
                              @index += 1
                            else
                              r12 = nil
                            end
                            if r12
                              r0 = r12
                            else
                              if has_terminal?('\G[\\x61-\\x69]', true, index)
                                r13 = true
                                @index += 1
                              else
                                r13 = nil
                              end
                              if r13
                                r0 = r13
                              else
                                if has_terminal?('\G[\\x6B-\\x7A]', true, index)
                                  r14 = true
                                  @index += 1
                                else
                                  r14 = nil
                                end
                                if r14
                                  r0 = r14
                                else
                                  @index = i0
                                  r0 = nil
                                end
                              end
                            end
                          end
                        end
                      end
                    end
                  end
                end
              end
            end
          end
        end
      end

      node_cache[:obs_zone][start_index] = r0

      r0
    end