There is no competition between applications of keybindings. Either your X server catches something (in most cases your Desktop) and reactions on a key (like pressing the volume up key) or the key is passed to the current application (i.e. the one that has focus). This is different from what I remember from Windows where you could have hot-keys that went to applications that did not have focus.

So you don't need to know which Alt+somekeyis already used by some other application, you only need to know if your desktop already catches it and does something with it.

There is no competition between applications of keybindings. Either your X server catches something (in most cases your Desktop) and reactions on a key (like pressing the volume up key) or the key is passed to the current application (i.e. the one that has focus). This is different from what I remember from Windows where you could have hot-keys that went to applications that did not have focus.

So you don't need to know which Alt+somekeyis already used by some other application, you only need to know if your desktop already catches it and does something with it.

If an application needs to know about a keyboard event e.g. pressing the Forward key on a Mediakeyboard, then the Desktop should catch that event and notify the application.