  The well-posedness of a system of partial differential equations and dynamic
boundary conditions, both of Cahn-Hilliard type, is discussed. The existence of
a weak solution and its continuous dependence on the data are proved using a
suitable setting for the conservation of a total mass in the bulk plus the
boundary. A very general class of double-well like potentials is allowed.
Moreover, some further regularity is obtained to guarantee the strong solution.
