The first form lists all of the currently-connected players, along with the amount of time they've been connected, the amount of time they've been idle, and their present location in the MOO.
The second form, in which a list of player names is given, shows information for just those players. For any listed players that are not connected, we show the last login time instead of the connect/idle times.
@who refers to the @who_location message (see "help messages") on each player's location in order to determine what should be printed in the location column. Pronoun substitutions are done on this string in the usual manner (see 'help pronouns'). The default value is "Verb not found" (i.e., the room name).
If the list of players to display is longer than 100, this command will not show its normal output, since it can be quite expensive to compute. In such cases, you might want to use the @users command instead; see "help @users" for more information.