(tkwait 'visibility name)
(tkwait 'window name)
The tkwait procedure waits for one of several things to happen, then it returns without taking any other actions. The return value is always an empty string. If the first argument is variable (or any abbreviation of it) then the second argument is the name of a global variable and the procedure waits for that variable to be modified. If the first argument is visibility (or any abbreviation of it) then the second argument is the name of a window and the tkwait procedure waits for a change in its visibility state (as indicated by the arrival of a VisibilityNotify event). This form is typically used to wait for a newly-created window to appear on the screen before taking some action. If the first argument is window (or any abbreviation of it) then the second argument is the name of a window and the tkwait procedure waits for that window to be destroyed. This form is typically used to wait for a user to finish interacting with a dialog box before using the result of that interaction.
While the tkwait procedure is waiting it processes events in the normal fashion, so the application will continue to respond to user interactions.