SECRETS lets you create a list of hints to help you find the secrets hidden in a level. This works with a special console command, secret, which will print these hints in different colors depending on their status; those that are found are in green, and the undiscovered ones in red.
Since all maps are listed in the same lump, each map has a ini-style section header in its name. A hint begins with the $ character, followed by either an s for a sector or a t for a trigger. Then there is the sector number or trigger TID, as appropriate, followed by a semi-colon ; and anything after is the hint text.
Each section may also contain lines without any secret info associated to them. Such lines will be printed yellow.
These hints are for the first three levels of Doom II:
[MAP01] $s41;#1 In the northernmost room, you see two switches; a near one on your right, and a far one on your left. The one on the right opens a small area to the northeast with some armor and health. $s8;#2 In the center room just south of the exit, there is a lift to the west. Go up the lift and hit space on the wall to the west, revealing a few imps and a switch which opens a door leading outside in the southeast corner of the center room, $s17;#3 Outside are some imps and a shotgun. $s57;#4 Once you hit the switch at the top of the lift, jump down onto the platform just east of the lift This will open a room with a rocket launcher to the north and east (#4). $s28;#5 A room with two imps and a stimpack, behind a hidden door on the south side of the east wall of the center room. [MAP02] $s79;#1 Just southwest of the red keycard (at the top of the steps) lies a room with blue armor. [MAP03] $s67;#1 In the main room, south of the two sets of stairs and the rocket launcher, is a small outcropping with a ledge. You can make it over the ledge if you run southeast at the right angle from the raised area west of the stairs.