In addition to the three main issues listed above, progress has also been made in the formal analysis of WF-in-DFT embedding methods, which can be approached from different perspectives . Perhaps the most fundamental DFT-type approach to WF-in-DFT embedding was presented by Wesolowski in 2008, regarding the embedded wavefunction as an alternative way of representing the electron density of the active system in terms of a multi-determinantal wavefunction of an interacting system of electrons, rather than a noninteracting, Kohn-Sham-like system . An extension of this work to non-variational embedded wavefunctions followed in 2019 . It was shown that the FDET energy functional can be expanded such that an energy correction from a non-variational, correlated wavefunction method can be employed if it is applied on top of a variational reference method. In addition, two terms linear in the correlation-induced density change ∆ρ(r) of the active system appear. The effect of the correlation potential in the context of this formalism was analyzed by Wesolowski as well . Essentially, neglecting the correlation energy functional and potential in the auxiliary system used to represent the active part leads to an energy expression correct to quadratic order in the correlationinduced energy change. A numerical study on interaction energies obtained in this way from DFT-embedded MP2 calculations indicated that hydrogen-bonded and dipole-dipole interaction-dominated complexes are rather well described, while the approximations used failed for interacting (dispersion-type) complexes, π-stacked systems, and in particular for charge-transfer complexes (mainly because of the basis-set incompleteness) .