About a programming tip

[Xue Fuqiao]

In (info "(elisp) Programming Tips"):

   * In `interactive', if you use a Lisp expression to produce a list
     of arguments, don't try to provide the "correct" default values for
     region or position arguments.
[...]
     You do not need to take such precautions when you use interactive
     specs `d', `m' and `r', because they make special arrangements to
     recompute the argument values on repetition of the command.

I'm confused with these two sentences.  The first sentence says that
"don't try to provide the 'correct' default values for region or
position arguments", but the second sentence says that "you don't need
to take such precautions when you use interactive specs `d', `m' and
`r'".  IIRC the specs `d', `m' and `r' are "region or position
arguments".  Where do I understand wrong, or is it a bug?  Thanks.

-- 
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao