  The effects of confinement resonances on photoelectron group delay (Wigner
time delay) following ionization of an atom encapsulated inside a C$_{60}$ cage
have been studied theoretically using both relativistic and non-relativistic
random phase approximations. The results indicate clearly the resonant
character of the confinement oscillations in time delay of the $4d$ shell of
Xe@C$_{60}$ and present a most direct manifestation of Wigner time delay. These
oscillations were missed in a previous theoretical investigation of Ar@C$_{60}$
[PRL 111, 203003 (2013)]
