Second, strategies for potential reconstruction have been refined and their use is becoming more and more common. Other strategies, which particularly aim at describing covalently bounded systems, include the 3-FDE or general buffer-fragment methods as well as energyor density-based many-body expansions combined with sDFT. An alternative that opens up an entirely new avenue is the replacement of the NAKP term by a projection operator in the Kohn-Sham-like equations for sDFT. While this projection-based embedding does, in the context of sDFT (i.e., a DFT-in-DFT embedding) not offer any efficiency advantages compared to a standard Kohn-Sham calculation, it plays important roles as a reference embedding method and in the framework of WF-in-DFT embedding. In this context, however, it has to be kept in mind that PbE is not a strict formal reference for FDE, since it works with projected orbital sets which are, in general, not the orbital sets that minimize the KS-kinetic energies of the subsystems for a given subsystem density.