In 2016, Chulhai and Jensen made a first attempt to transfer the concept of external orthogonality to subsystem TDDFT . In their work, however, a symmetric eigenvalue problem was derived by implicitly assuming that the PbE kernel contributions are identical for the A and B matrices, which leads to deviations from corresponding Kohn-Sham supersystem results. The "exact" version of subsystem TDDFT was derived for all three different projection operators considered above in work from our (JN's) lab in 2018 . It could be demonstrated that this exact sTDDFT (when using the full supermolecular basis in each subsystem calculation and considering the full space of orbital transitions of all subsystems) is equivalent to a supermolecular TDDFT formulated in localized molecular orbitals (LMO). Hence, all three major problems mentioned above can be solved by this approach. Another benefit of using PbE is that XC approximations incorporating exact exchange contributions can be easily used, which is problematic if the subsystem orbitals are not externally orthogonal. This is important for TDDFT-type calculations, for which hybrid functionals and in particular range-separated hybrids are very popular.