anchor.diff:         "tab" 'insert-candidate
          "M-h" 'minibuffer-history
          "C-space" 'minibuffer-toggle-mark
  -       "shift-space" 'minibuffer-toggle-mark
  +       "shift-space" 'minibuffer-toggle-mark-backwards
          "M-space" 'minibuffer-toggle-mark
          "M-a" 'minibuffer-mark-all
          "M-u" 'minibuffer-unmark-all))
  
positive.code:         (setf (input-cursor-position minibuffer) 0)
          (insert input minibuffer)))))
  
  (define-command minibuffer-toggle-mark (&optional (minibuffer (current-minibuffer)))
    "Toggle candidate.
  Only available if minibuffer `multi-selection-p' is non-nil."
    (when (multi-selection-p minibuffer)
      (with-slots (completions completion-cursor marked-completions) minibuffer
        (let ((candidate (nth completion-cursor completions)))
  
negative.code:           (_ (push candidate marked-completions)))))
      (state-changed minibuffer)
      (update-display minibuffer)
      (match direction
        (:next (select-next minibuffer))
        (:previous (select-previous minibuffer)))))
  
  (define-command minibuffer-toggle-mark-backwards (&key (minibuffer (current-minibuffer)))
    "Toggle candidate and select previous candidate.
  See `minibuffer-toggle-mark'. "
    (minibuffer-toggle-mark :minibuffer minibuffer :direction :previous))
  
  (define-command minibuffer-mark-all (&optional (minibuffer (current-minibuffer)))
    "Mark all visible candidates.
  