# File lib/org-ruby/output_buffer.rb, line 115
    def get_next_headline_number(level)
      raise "Headline level not valid: #{level}" if level <= 0
      while level > @headline_number_stack.length do
        @headline_number_stack.push 0
      end
      while level < @headline_number_stack.length do
        @headline_number_stack.pop
      end
      raise "Oops, shouldn't happen" unless level == @headline_number_stack.length
      @headline_number_stack[@headline_number_stack.length - 1] += 1
      @headline_number_stack.join(".")
    end