Displays question in string s and returns true or false depending upon which button is clicked. See #YESNO for more options. If more than two buttons are displayed, the result is the button number, making this useful in conjunction with #CASE. With only two buttons, 0 or 1 is returned, making this useful in conjunction with #IF.
Example:
#IF %yesno("Do you really want to quit now?") {quit;y} {resume}