  For the discretisation of $H_{div}$-functions on rectangular meshes there are
at least three families of elements, namely Raviart-Thomas-,
Brezzi-Douglas-Marini- and Arnold-Boffi-Falk-elements. In order to prove
convergence of a numerical method using them, sharp interpolation error
estimates are important. We provide them here in an anisotropic setting for the
$H_{div}$-norm.
