  Comparison with La$_{2-z-x}$Nd$_z$Sr$_x$CuO$_4$ ($z=0, 0.4$) shows that the
retrograde doping dependence of charge order in
La$_{1.8-x}$Eu$_{0.2}$Sr$_x$CuO$_4$ must be caused by a mechanism transcending
the common charge-order generation in the hole-doped lanthanum cuprates. This
could be a bond-stretching phonon with comparable momentum, $q \sim 0.24$
r.l.u., as observed in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$.
