bug#11361: 24.1.50; doc string of `yank-pop-change-selection'

[Eli Zaretskii]

> From: "Drew Adams" <drew.adams@oracle.com>
> Date: Fri, 27 Apr 2012 07:18:24 -0700
> 
> This is the entire doc string:
>  
> "If non-nil, rotating the kill ring changes the window system
> selection."
>
> That is worthless, to use a polite word.

I don't know why you decided to go after this doc string.  It is quite
clear.

> What on earth does "changes the window system selection"?

Would "sets the window system's primary selection" be clearer?

> What is "the window system selection"?

"Selection" is widely accepted terminology.  From the Emacs Glossary:

  Primary Selection
       The primary selection is one particular X selection (q.v.); it is
       the selection that most X applications use for transferring text
       to and from other applications.

       The Emacs kill commands set the primary selection and the yank
       command uses the primary selection when appropriate.  *Note
       Killing::.

> How is it changed by setting this to non-nil?  What do nil and non-nil
> actually do?

The nil value doesn't do anything, obviously.