the first time i learnt about chess is the famous Fischer-Spassky match in 1972, at that time, the player could seal his move inside an envelop to adjourn the game, and left the work for his second to analyze the position of the unfinished game, the player just continue to play the moves next day that his second provided for him. i also notice that the player could walk away from the playing board anytime he wanted.
as a chinese chess player, i was very surprised that this kind of action would be allowed in chess match, it is 100% prohibited in chinese chess match.
now the " sealing move inside an envelop after 40 moves" is no more a rule.