  With the example of hexagonal boron nitride, we demonstrate how the character
of electron-hole (e-h) pairs in van der Waals bound low-dimensional systems is
driven by layer stacking. Four types of excitons appear, with either a two- or
three-dimensional spatial extension. Electron and hole distributions are either
overlapping or exhibit a charge-transfer nature. We discuss under which
structural and symmetry conditions they appear and they are either dark or
bright. This analysis provides the key elements to identify, predict, and
possibly tailor the character of e-h pairs in van der Waals materials.
