In this section:
Sometimes, especially when an edit box is displayed, it is desirable to control the closure of a window. %cc (Control Closure) takes a call-back function as its argument. This function is called before the window closes (for whatever reason). If it returns a positive value the window is not closed. If a grave is used (%`cc) then the associated call-back function is called after the window is closed. A single window could use both %cc and %`cc.