(a) Problem schematic in the assumed 2-D (x, z) reference system (with geometry and field quantities independent of y). We consider a transversely-magnetic-polarized plane-wave (with wavevector k) propagating in a homogenous space filled up by a nonlocal, nonmagnetic, anisotropic medium characterized by a relative-permittivity constitutive tensor . (b) Qualitative example of ideal dispersion surface [cf. Eq. (3)] pertaining to the assumed constitutive blueprints [cf. Eqs. (4) and (6), with ]. (c) Corresponding dispersion diagram (k_x = 0 cut), with the black-cross marker indicating the DBE-type stationary point.