  We present a kinetic energy tensor that unifies a scalar kinetic energy
density commonly used in meta-Generalized Gradient Approximation functionals
and the vorticity density that appears in paramagnetic
current-density-functional theory. Both types of functionals can thus be
subsumed as special cases of a novel functional form that is naturally placed
on the third rung of Jacob's ladder. Moreover, the kinetic energy tensor is
related to the exchange hole curvature, is gauge invariant, and has very
clearcut $N$-representability conditions. The latter conditions enable the
definition of effective number of non-negligible orbitals. Whereas quantities
such as the Electron Localization Function can discriminate effective
one-orbital regions from other regions, the present kinetic energy tensor can
discriminate between one-, two-, three-, and four-or-more orbital regions.
