|[ < ]||[ > ]||[ << ]||[ Up ]||[ >> ]||[Top]||[Contents]||[Index]||[ ? ]|
This command actually moves you to the environment of the specified player to perform the given command. The move is a forced move so that weight accounting and destination tests aren't performed, but you are still actually moved there, so any triggers on entering and leaving will be notified.
At <player name> <command>
Usually there's better ways of doing things than by this command, however, for some problems there are no substitues. A good example is that you want to take a look in the room that a player, for instance Adam, is standing in:
At adam look
You might want to take the precaution of going invisible before doing it so that most player-oriented output is forestalled.