# File lib/treetop/compiler/metagrammar.rb, line 1495
      def _nt_label
        start_index = index
        if node_cache[:label].has_key?(index)
          cached = node_cache[:label][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, s2 = index, []
        r3 = _nt_alpha_char
        s2 << r3
        if r3
          s4, i4 = [], index
          loop do
            r5 = _nt_alphanumeric_char
            if r5
              s4 << r5
            else
              break
            end
          end
          r4 = instantiate_node(SyntaxNode,input, i4...index, s4)
          s2 << r4
        end
        if s2.last
          r2 = instantiate_node(SyntaxNode,input, i2...index, s2)
          r2.extend(Label0)
        else
          @index = i2
          r2 = nil
        end
        s1 << r2
        if r2
          if has_terminal?(':', false, index)
            r6 = instantiate_node(SyntaxNode,input, index...(index + 1))
            @index += 1
          else
            terminal_parse_failure(':')
            r6 = nil
          end
          s1 << r6
        end
        if s1.last
          r1 = instantiate_node(SyntaxNode,input, i1...index, s1)
          r1.extend(Label1)
          r1.extend(Label2)
        else
          @index = i1
          r1 = nil
        end
        if r1
          r0 = r1
        else
          if has_terminal?('', false, index)
            r7 = instantiate_node(SyntaxNode,input, index...(index + 0))
            r7.extend(Label3)
            @index += 0
          else
            terminal_parse_failure('')
            r7 = nil
          end
          if r7
            r0 = r7
          else
            @index = i0
            r0 = nil
          end
        end

        node_cache[:label][start_index] = r0

        r0
      end