# File lib/mail/parsers/rfc2822.rb, line 2342
    def _nt_quoted_string
      start_index = index
      if node_cache[:quoted_string].has_key?(index)
        cached = node_cache[:quoted_string][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_DQUOTE
        s0 << r3
        if r3
          s4, i4 = [], index
          loop do
            i5, s5 = index, []
            r7 = _nt_FWS
            if r7
              r6 = r7
            else
              r6 = instantiate_node(SyntaxNode,input, index...index)
            end
            s5 << r6
            if r6
              r8 = _nt_qcontent
              s5 << r8
            end
            if s5.last
              r5 = instantiate_node(SyntaxNode,input, i5...index, s5)
              r5.extend(QuotedString0)
            else
              @index = i5
              r5 = nil
            end
            if r5
              s4 << r5
            else
              break
            end
          end
          if s4.empty?
            @index = i4
            r4 = nil
          else
            r4 = instantiate_node(SyntaxNode,input, i4...index, s4)
          end
          s0 << r4
          if r4
            r10 = _nt_FWS
            if r10
              r9 = r10
            else
              r9 = instantiate_node(SyntaxNode,input, index...index)
            end
            s0 << r9
            if r9
              r11 = _nt_DQUOTE
              s0 << r11
              if r11
                r13 = _nt_CFWS
                if r13
                  r12 = r13
                else
                  r12 = instantiate_node(SyntaxNode,input, index...index)
                end
                s0 << r12
              end
            end
          end
        end
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(QuotedString1)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:quoted_string][start_index] = r0

      r0
    end