Log energy is on the horizontal axis, while time is along the vertical. The energy of the peak in $\nu F_{\nu}$ (i.e.: [$E_{\rm peak}$]{}) is traced over time by the dashed red line and can clearly be seen to exhibit a hard-to-soft trend, as indicated by movement toward the left in the plot. A vertical cut or band corresponds to a specific energy. The pulse peaks appear later in the lower energy bands, which is the source of the spectral lag. At the same time, the temporal power-law nature of [$E_{\rm peak}$]{} ensures that an increasing number of spectra with similar [$E_{\rm peak}$]{} values are found in a given accumulation time with respect to similar accumulations at the start of the pulse, where the spectra are varying more rapidly. This is the source of the increase in pulse temporal width with lower energy. It is interesting to speculate how this might be extended in the opposite direction in time with respect to the highest peak energies. The observed trend is that the pulse width becomes increasingly narrow with higher energies at the same time that the pulse peak lag gets shorter, so that the temporal width approaches zero. The limiting 