Grabs are local by default. During global grabs the window manager will not receive pointer events either. Tk grabs the keyboard so that all keyboard events are always sent to the grabbing application. The focus method is still used to determine which window in the application receives the keyboard events. The keyboard grab is released when the grab is released.
Grabs apply to particular displays.
If an application has windows on multiple displays then it can establish a separate grab on each display. The grab on a particular display affects only the windows on that display. It is possible for different applications on a single display to have simultaneous local grabs, but only one application can have a global grab on a given display at once. Returns an empty string. Returns an empty string.