The rigorous range separation of electron correlation has led to a proliferation of wave-function methods using short-range exchange-correlation functionals as an inexpensive way of accounting for dynamical (short-range) correlation, thereby improving their accuracy and/or efficiency. A promising direction of development of DFT via its merger with WFT is enabled by gaining access to a correlated two-particle local function -the ontop pair density -which can be used as a variable in correlation functionals in addition to the electron density; see, for example, ref. 213 and contribution (4.1.1).