<<< mml $${\phantom{z}S}_t^7=S_t^7$$ >>> native [ ESubsup (EGrouped [ EPhantom (EIdentifier "z") , EIdentifier "S" ]) (EIdentifier "t") (ENumber "7") , ESymbol Rel "=" , ESubsup (EIdentifier "S") (EIdentifier "t") (ENumber "7") ]