“…While the companion article [8] will be concerned with the derivation of computable a posteriori error bounds, and their implementation within automatic hp-anisotropic adaptive software, the current paper will focus on a priori error estimation. To this end, the proofs of the a priori error bounds presented in this article are based on exploiting the analysis developed in [10], which assumed that the underlying computational mesh is shape-regular and that the polynomial approximation orders are isotropic, together with the anisotropic hp-approximation results presented in [6]; for related work on anisotropic approximation theory, see [1,3,4,7,15,16], for example, and the references cited therein. We also refer to the recent article [7], where the goal-oriented error analysis of the interior penalty DGFEM on anisotropic computational meshes, assuming that the polynomial degree is kept fixed, has been developed.…”