Comment on Intensity modulation of the Shirley background of the Cr3p spectra with photon energies around the Cr2p edge, by A Herrera-Gomez, D Cabrera-German, A D Dutol et al, Surface Interface Anal, 2018;50:246-252

We show that, while the Shirley background lacks a theoretical basis, its use satisfies the condition for the proper modeling of all these backgrounds when properly applied. We present these four conditions of applicability, discuss their use, and indicate where their lack of use gives misleading results.