anchor.diff:  
     :color
        A color string. Either HTML-style #RRGGBB or #AARRGGBB, or a color name."
  -  `(box
  +  `(:box
       ,@(when start (list :start start))
       ,@(when end (list :end end))
       ,@(when filled-supplied-p (list :filled filled))
  
positive.code: serialized via an encapsulated write lock to prevent contexts from overwriting
  one another, so calls should be made as short as possible."
    `(with-mutex (*write-lock*)
       (draw-it *command-stream* ,@body)))
  
  (defun box (&key start end (filled nil filled-supplied-p) color)
    "Generates a Gypsum drawing primitive to draw a box with the given parameters.
  
negative.code: (in-package :cl-gypsum-client)
  
  (export '(listen
            with-gypsum-context
            box
            text
  