Involutive deformations of the regular part of a normal surface

We define the property of involutivity for deformations of complex structure on a manifold X, with particular reference to the regular part of a normal surface. Our main result is a sufficient condition for involutivity in terms of a "Ə-Cartan formula", previously examined in [3] in the more special context of cone singularities. By way of examples we show that some involutive deformations of the regular part determine a subspace, if not the entire versal space, of flat deformations of normal surface singularities, while others may determine Stein surfaces which lie outside the versal space of flat deformations of a given normal surface.