anchor.diff:  (defclass-export download-data-path (data-path) ; TODO: Rename to downloads-data-path?
     ((ref :initform "download")))
   
  +(declaim (ftype (function (string) (or string null)) find-ref-path))
   (defun find-ref-path (ref)
  +  "Return the value of the REF found in `*options*'s `:with-path'.
  +Example: when passed command line option --with-path foo=bar,
  +\(find-ref-path \"foo\") return \"bar\"."
     (second
      (assoc ref
             (loop for (opt value . _) on *options*
  
positive.code: 
  (export-always 'expand-default-path)
  (declaim (ftype (function (data-path &key (:root string)) (or string null)) expand-default-path))
  (defun expand-default-path (path &key (root (namestring (or (dirname path)
                                                              (uiop:xdg-data-home +data-root+)))))
    "Derive file from command line option or PATH.
  If PATH `ref' is specified in the `:with-path' command line option, use it in
  place of PATH `basename'.
  
negative.code: (defclass-export data-path ()
    ((dirname :initarg :dirname
              :accessor dirname
              :type (or string pathname)
              :initform ""
              :documentation "The directory of `basename'.")
     (basename :initarg :basename
               :accessor basename
               :type (or string pathname)
               :initform ""
               :documentation "The basename of data-path.
  It can be appended with an extension if necessary.
  