How does patching keybindings work?

[rieje]

I'm not really a programmer, so I'm hoping you can help me understand how the patch for adding C-v for pasting from primary selection works. By default, C-Y pastes from primary selection, as defined:

case XK_Y:
XConvertSelection(dpy, (ev->state & ShiftMask) ? clip : XA_PRIMARY,
           utf8, utf8, win, CurrentTime);
return;

So I simply assumed creating the same entry for XK_v would do it:

case XK_v:
XConvertSelection(dpy, (ev->state & ShiftMask) ? clip : XA_PRIMARY,
           utf8, utf8, win, CurrentTime);
return;

However, it seems to apply to C-V instead. Your patch works fine and the difference is at line 27 where you have the exclamation point at !(ev->state & ShiftMask). What's the context of that and why is it needed here but not for case XK_Y? I assume it's something to do with shift key being used for capital Y vs. not being used for lowercase v. Also, why is it necessary to create an empty case for `case XK_v?

Much appreciated.

P.S. I'm thinking of changing the binding of C-j and C-k for down/up for vim-like behavior and C-l for ~ C-; for Enter to stay on home row but am still deciding if it's worth it and if it's trivial to implement it.