I want to take a shot at answering my first question on this forum. If I understand your question right, you are referring to concepts of "clipboard" and "primary". If not - sorry, I am wrong.
Note: After the comment by @jjaderberg below, I decided to clarify why I assumed that xterm_clipboard in vim is Primary. To be sure I looked up Clipboard definition in xterm manual page. I was basically looking for other definitions of the word 'clipboard' in xterm context besides those explained below. Since I did not find anything, I made an assumption that xterm_clipboard in vim is Primary in X, since Vim's
:help xterm_clipboard defines it as just:
+xterm_clipboard Unix only: xterm clipboard handling
Every X.org application (X window system implementation, as you know) has a shared copy/paste buffer called Primary. That's where xterm, rxvt and other X applications copy selection, which is cleared once you make another selection. You can see what is in your 'primary' by running:
xsel -p -o
This will print contents of your Primary buffer (note,
xsel may not be installed by default). Another copy/paste buffer is called Clipboard, which is what you use when you do
ctrl+c/ctrl+v. You can see what's in it:
xsel -b -o
In vim (on Linux at least), register
* stores Primary and register
+ stores Clipboard. So if you make a selection in xterm and then in vim do
"*p then you will insert what you selected in xterm.
"+p will insert clipboard. (I think, if you copy something into clipboard you will clobber Primary, but I am not 100% sure, maybe someone can pitch in on this.)
I am not sure, how this relates to mouse, but I did notice that the visual selection that's done by mouse (with
mouse=a) in vim in xterm also goes into
* register and hence in Primary.
I also, can't answer for sure about default availability of this functionality, but I want to assume (after rebuilding vim7.4 many times) that in the vast majority of cases they are compiled in by default. If anyone has more input on this, please edit this bit too.
You can read more about this on Arch wiki.
Thanks for reading. Sorry, if I misunderstood. Hopefully, this helped a little. Cheers. :)