Most levels contain '''Secretssecrets''' can mean several things:. At the end of each level, the percentage of secrets found is displayed on the [[intermission screen]].
*Areas of a level Secrets are usually areas that are hidden (to some extent). UsuallyOften, there is some clue about a secret area, such as an off-color [[wall]] that is actually a [[door]]. By convention, most levels are designed so that it is not necessary to find any of the secret areas to complete a the level.
*A special [[sector]] type (type 9), is used to calculate the secrets-found percentage displayed at the end of each level. The number of type 9 sectors in the level is the total number of secrets. When a player first enters a type 9 sector, the number of secrets found is incremented by one. A secret (or "hidden") area may encompass any number of sectors, but will normally contain only one sector of type 9 in order to give the secrets-found percentage a straightforward interpretation. Some [[source ports]] use the type 9 sector to trigger an announcement such as "<small>A SECRET HAS BEEN REVEALED</small>" or to play a sound, but the original game does not give any indication until the [[intermission screen]].
*A [[linedefLinedef]] s have a ''secret'' flag bit (bit 5). This flag makes a two-sided linedef appear on the [[automap]] in red instead of yellow, that is, just like a single-sided linedef. This is It used to hide entrances to secret areas on the automap, but has nothing to do with the calculation of the secrets percentage displayed at . In [[vanilla Doom]], a secrets percentage of 0% is ambiguous. Normally, it means the end player found none of each the secrets, but it could also mean that the levelhas no secrets to find. Some source ports display 100% in the latter case, to indicate that the player has done as well as possible.
==See also==
