  Our calculations of ferromagnetic spin chains on s-wave superconductors show
that the energy oscillations of edge states with the chain's length are due to
a moir\'e pattern emerging from Friedel-like oscillations and the discreteness
of the spin-chain lattice. By modifying the spin lattice, the moir\'e
dispersion of edge states can be controlled. In particular, we can engineer
non-dispersive edge states that remain at fixed energy regardless of the size
distribution of the spin chains. This is an important step in the study of edge
states of spin chains that can be fabricated with a certain size dispersion.
