Understanding kill-ring-save

[Kaushal <kaushal.modi@gmail.com>]

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Hi all,

I was trying to understand the basic function `kill-ring-save` and came up
with this question on emacs.SE: http://emacs.stackexchange.com/q/14937/115

I will reiterate the question(s) that arose over here:

- kill-ring-save has an optional argument REGION
- That arg is set internally as (prefix-numeric-value current-prefix-arg)
- So whether or not I use C-u, REGION will be a non-nil value, either 1 (if
I simply do M-w) or 4 (if I do C-u M-w).

Questions:

- Under what circumstances will the REGION value stay nil?
- When can `prefix-numeric-value` function return nil? Or can it?

If the answers to the above 2 questions are never, never and no, why do we
have the REGION argument? Or can that be set only in elisp? Example:
(kill-ring-save (region-beginning) (region-end) nil)

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