anchor.diff:                                 +itunes-title+ +itunes-tool+ +itunes-writer+)
                            :test #'string=)
                    (stream-read-utf-8-string mp4-file (- (atom-size me) 16)))
  +
   
                   ((member (atom-type parent)
                            (list +itunes-track+ +itunes-track-n+ +itunes-disk+)
  
positive.code:   (with-slots (atom-size atom-type atom-version atom-flags atom-value) me
      (setf atom-version (stream-read-u8 mp4-file)
            atom-flags   (stream-read-u24 mp4-file))
      (assert (= 0 (stream-read-u32 mp4-file)) ()
              "a data atom lacks the required null field")
  
      (setf atom-value
            (cond ((member (atom-type parent)
                           (list +itunes-album+ +itunes-album-artist+ +itunes-artist+
  
negative.code:        (write-char (code-char ,(as-octet l3)) s)
         (write-char (code-char ,(as-octet l4)) s))))
  
  ;;;; Atom names/ids
  (defconstant* +root+                  (mk-mp4-atom-type #\R #\O #\O #\T)  "fake root for tree")
  (defconstant* +itunes-album+          (mk-mp4-atom-type #xa9 #\a #\l #\b) "text: album name")
  (defconstant* +itunes-album-artist+   (mk-mp4-atom-type #\a  #\A #\R #\T) "text: album artist")
  