anchor.diff:      (values (when suggestion (prompter:value suggestion)) source)))
   
   (defun show-prompt-buffer (prompt-buffer &key height)
  -  "Show the last active prompt-buffer, if any."
  +  "Show the last active prompt-buffer, if any.
  +This is a low-level display function.
  +See also `hide-prompt-buffer'."
     ;; TODO: Add method that returns if there is only 1 source with no filter.
     (when prompt-buffer
       (push prompt-buffer (active-prompt-buffers (window prompt-buffer)))
  
positive.code:            (ps:lisp input))))
    (update-prompt-input prompt-buffer input))
  
  (defun wait-on-prompt-buffer (prompt-buffer)
    "Block and return PROMPT-BUFFER results."
    (when (prompt-buffer-p prompt-buffer)
      (calispel:fair-alt
        ((calispel:? (prompter:result-channel prompt-buffer) results)
         (hide-prompt-buffer prompt-buffer)
  
negative.code:      (or height
           (prompt-buffer-open-height (window prompt-buffer))))))
  
  (export-always 'hide-prompt-buffer)     ; TODO: Unexport for 3.0.
  (defun hide-prompt-buffer (prompt-buffer)
    "Hide PROMPT-BUFFER, display next active one.
  This is a low-level display function.
  See also `show-prompt-buffer'."
    (let ((window (window prompt-buffer)))
      ;; Note that PROMPT-BUFFER is not necessarily first in the list, e.g. a new
      ;; prompt-buffer was invoked before the old one reaches here.
  