When a file is visited, the file's class is found. A directory
may be assigned a class using `dir-locals-set-directory-class'.
Then variables are set in the file's buffer according to the
-class' LIST. The list is processed in order.
+VARIABLES list of the class. The list is processed in order.
* If the element is of the form (MAJOR-MODE . ALIST), and the
buffer's major mode is derived from MAJOR-MODE (as determined