anchor.diff:  (defun collada-parse-source (dom node)
     (declare (ignore dom))
     (assert (string= (dom:tag-name node) "source"))
  -  (let* ((array-node (collada-node-singleton node "float_array"))
  +  (let* ((array-node (dom-select-tag node "float_array" :direct t :singleton t))
            (array-values (collada-node-floats array-node))
  -         (technique-node (collada-node-singleton node "technique_common"))
  -         (accessor-node (collada-node-singleton technique-node "accessor"))
  +         (technique-node (dom-select-tag node "technique_common" :direct t :singleton t))
  +         (accessor-node (dom-select-tag technique-node "accessor" :direct t :singleton t))
            (stride (if (dom:has-attribute accessor-node "stride")
                        (parse-integer (dom:get-attribute accessor-node "stride"))
                        1)))
  
positive.code: 
  (defun collada-parse-vertices (dom node)
    (assert (string= (dom:tag-name node) "vertices"))
    (let ((input (collada-node-singleton node "input")))
      (assert (and (dom:has-attribute input "semantic")
                   (string= (dom:get-attribute input "semantic")
                            "POSITION")))
  
negative.code: (defun collada-povray (&key
                           (dom *collada-dom*)
                           file)
    (let* ((result (pov-sequence
                   (let* ((node (dom-select-tag dom "library_visual_scenes" :singleton t)))
                     (collada-povray-visual-scene dom node)))))
      (if file
          (with-open-file (s file :direction :output :if-exists :supersede)
  