anchor.diff:      (setf (slot-value term 'width) (truncate (or width (- (second dims) (x-offset term))) 8)
             (slot-value term 'height) (truncate (or height (- (first dims) (y-offset term))) 16))
       (sys.graphics::bitset (* (terminal-height term) 16) (* (terminal-width term) 8)
  -                          #xFF000000 fb
  +                          (logior #xFF000000 (background-colour term)) fb
                             (y-offset term) (x-offset term))))
   
   (defun report-unknown-escape (term)
  
positive.code:   (when (and (<= 0 (y-pos term) (1- (terminal-height term)))
               (< left right))
      (sys.graphics::bitset 16 (* (- right left) 8)
                            #xFF000000 (terminal-framebuffer term)
                            (+ (* (y-pos term) 16) (y-offset term)) (+ (* left 8) (x-offset term)))))
  
  (defun xterm-initial (terminal byte)
    "Initial state."
  
negative.code:   (setf bottom (clamp bottom 0 (terminal-height term)))
    (when (< top bottom)
      (sys.graphics::bitset (* (- bottom top) 16) (* (terminal-width term) 8)
                            (logior #xFF000000 (background-colour term)) (terminal-framebuffer term)
                            (+ (* top 16) (y-offset term)) (x-offset term))))
  
  (defun erase (term left right)
  