Tietze type extensions for absolutely continuous functions in the plane

It is an open problem whether one can always extend an absolutely continuous function (in the sense of Ashton and Doust) on a compact subset of the plane to a larger compact set. In this paper we show that this can be done for a large family of initial domains whose components consist of polygons and convex curves. An application is given to the spectral theory of $AC(\sigma)$ operators.