anchor.diff:                                  (string= class "MuPDF"))))
     "List of predicates against which windows are grouped")
   
  -(defun add (window)
  +(defun plus (window)
     "Add window to the list of managed windows. Take care of grouping
   and don't add window already in the list."
     (let ((grouper (find-if #'(lambda (f) (funcall f window)) *groupers*)))
  
positive.code:                (:map-notify
                  (window override-redirect-p)
                  (unless override-redirect-p
                    (focus (add window))))
                 (:destroy-notify
                  (window)
                  (focus (destroy window)))))
        (ungrab-button *root* (code *move*) :modifiers (state *move*))
        (ungrab-button *root* (code *resize*) :modifiers (state *resize*))
        (ungrab-button *root* (code *kill*) :modifiers (state *kill*))
  
negative.code:     (loop for w in (query-tree *root*) do
           (when (and (eql (window-map-state w) :viewable)
                      (eql (window-override-redirect w) :off))
             (plus w)))
  
      (setf (window-event-mask *root*) '(:substructure-notify))
  
  