A mess in kill-region?

[Marcin Borkowski <mbork@mbork.pl>]

Hi there,

I don't have the time now to study this deeper, but if this something
non-obvious, I can try to dig into it (maybe in a few days).

Here's the problem.  This is taken from `kill-region':

(if region
    (funcall region-extract-function 'delete)
  (filter-buffer-substring beg end 'delete))

But this is the definition of `region-extract-function':

(defvar region-extract-function
  (lambda (delete)
    (when (region-beginning)
      (if (eq delete 'delete-only)
          (delete-region (region-beginning) (region-end))
        (filter-buffer-substring (region-beginning) (region-end) delete))))
  "Function to get the region's content.
Called with one argument DELETE.
If DELETE is `delete-only', then only delete the region and the return value
is undefined.  If DELETE is nil, just return the content as a string.
If anything else, delete the region and return its content as a string.")

So I guess that the argument of 'delete in `kill-region' is misleading
at least and maybe buggy.

And btw: what exactly is the meaning of the third argument to
`kill-region'?  The "explanation" is the docstring looks like a joke to
me;-).

PS. GNU Emacs 25.0.50.1 (i686-pc-linux-gnu, GTK+ Version 3.10.8) of 2015-01-02

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University