add_line_numbers

# File lib/rdoc/generator/markup.rb, line 87
  def add_line_numbers(src)
    return unless src.sub!(/\A(.*)(, line (\d+))/, '\1')
    first = $3.to_i - 1
    last  = first + src.count("\n")
    size = last.to_s.length

    line = first
    src.gsub!(/^/) do
      res = if line == first then
              " " * (size + 1)
            else
              "<span class=\"line-num\">%2$*1$d</span> " % [size, line]
            end

      line += 1
      res
    end
  end