# File gtk/sample/gtk-demo/main.rb, line 248
    def fontify(start_iter = @source_buffer.start_iter,
                end_iter = @source_buffer.end_iter)
      str = @source_buffer.get_text(start_iter, end_iter, true)

      tokenizer = RubyTokonizer.new
      tokenizer.tokenize(str, start_iter.offset) do |tag, start, last|
        @source_buffer.apply_tag(tag.to_s,
                                 @source_buffer.get_iter_at_offset(start),
                                 @source_buffer.get_iter_at_offset(last))
      end
    end