[Mark S 2014]

My textbook doesn't seem to show the NO₂ group exerting a -M effect upon the carbocation when a new substituent group is attached to nitrobenzene. It simply shows that it meta-directs because it is the only position that does not allow the positive charge to be at the 1 position. It shows resonance withdrawing electrons away from the ring BEFORE it is substituted, should it not show how resonance effects the carbocation when the new sub group is attached too ?