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: - Otherwise expand to 'ROOT/basename.lisp' or 'ROOT/basname' if the basename
    already contains a period."
    (let ((name (match (find-ref-path (ref path))
                  (nil (basename path))
                  (m m))))
      (cond
        ((uiop:emptyp name)
         root)
        ((search "/" name)
         (namestring name))
        (t
         (let ((fullname (str:concat root "/" (namestring name))))
           (unless (search "." name)
             (setf fullname (str:concat fullname ".lisp")))
           fullname)))))
  
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.
  