Nontrivial Massey products on compact K\"ahler manifolds

We show that the bigraded quasi-isomorphism type of the bigraded, bidifferential algebra of forms on a compact K\"ahler manifold generally contains more information than the de Rham cohomology algebra with its real Hodge structure. More precisely, on any closed Riemann surface of genus at least two, there is a nontrivial ABC-Massey product. Furthermore, starting from dimension three, there are simply connected projective manifolds with a nonzero ABC-Massey product of three divisor classes. In particular, compact K\"ahler manifolds are generally not formal in the sense of pluripotential homotopy theory.