Developer Commentary is a "value added" feature embedded in many of Valve's games, including Left 4 Dead and Left 4 Dead 2. This feature can be accessed through the Extras section of the game.
Usage[]
Its purpose is to enhance a player's "permission to believe" by providing an opportunity to enjoy an informed glimpse from behind the scenes and to develop an appreciation of the thoughts, ideas, technology and processes used to develop the game. Developer commentaries sometimes also include specific facts pertaining to the game's canon; for example, one commentary states that Francis is six-feet five-inches tall.
After accessing the Developer Commentary mode, a player is invited to travel through a campaign chapter in perfect safety as all Infected will only attack the AI Bot Survivors. At intervals, there are icons called Commentary Nodes (refer the illustration opposite) which trigger a specific audio comment when the player presses the "use" key while looking at the icon.
Some Commentary Nodes do more than simply play a recorded narrative and go so far as to spawn objects, characters and even scripted events pertaining to a specific fact. In Left 4 Dead and Left 4 Dead 2, the Developer Commentary takes place in the campaigns No Mercy and The Parish respectively.
The following pages provide more in-depth coverage of the developer commentaries in each game: