+
+# in cook and par,
+# a, aN anything including -
+# t, tN temporary value (in our db, no logged in user yet)
+# y, yN value corresponds to logged-in user
+# n, nN value not in our db
+# x, xN t or y
+# - no value supplied
+# if N differs the case applies only when the two values differ
+# (eg, a1 y2 does not apply when the logged-in value is supplied twice)
+
+# "stale session" means request originates from a page from a login
+# session which has been revoked (eg by logout); "cleared session"
+# means request originates from a browser which has a different (or
+# no) cookie.
+