Recent advances in light sources make it timely to consider one of the next natural steps in time-resolved spectroscopy, which is to probe the fastest time scales relevant to chemistry, the motions of valence electrons. Anticipating the experimental realization of attosecond pulses with photon energies of a few hundred eV to 1 keV, we have developed a simple theory which connects the evolution of a non-stationary electronic state to an XUV/X-ray probe signal. The electronic states we wish to follow evolve on time scales of a few femtoseconds. The essential principle is that the dynamic valence occupancy structure of these states can be probed, resolved in both space and time, by taking advantage of the inherent locality of core--valence transitions and the comparatively short time scale on which they can be produced. The development from the complexities of many-body theory to an intuitive picture of dynamic local occupancy structure will be presented along with some key numerical results, which we hope to compare with future experiments.