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The commentary node model used in the Half-Life 2
Commentary node model skin used after the commentary has been listened to.
The in-game Developer commentary, turned off by default, is intended to give players an insight into the development process of the game, as well as offering interesting information which might not have been obvious initially.
Valve introduced the feature in Half-Life 2: Lost Coast and later acquainted it with Episode One, Episode Two, Portal, Portal 2, Left 4 Dead, Left 4 Dead 2 and Team Fortress 2.
- The icons can be activated by enabling developer commentary from the options dialog box. Pressing the
USE key whilst the crosshair is hovering over the icon in-game causes them to begin playing, and the same key again stops the sound. Distance from the icon is not a factor, as an icon can be activated from any proximity as long as it is visible.
- The icons play recordings of Valve team members or voice actors, who talk about behind-the-scenes information, including how or why they made the map, an enemy, a character, or a storyline idea, what happened in the earlier iterations of the map or area, and in the voice actors' case, how they coped with the voice acting.
- Sometimes, the nodes will take control of the player's camera in order to show different areas or techniques. An example of this can be seen in Lost Coast; the screen is separated down the center to show the difference in rendering with HDR enabled and disabled.
- Activating a commentary node will also activate a number of side effects depending on the game: temporarily disabling the game's AI, as in in Lost Coast, or rendering the player invulnerable to enemy attacks, as in the Half Life 2 Episodes. To counter this, achievements cannot be achieved whilst in commentary mode (except in the case of Portal 2's Single Player), as it makes the game easier. Activating a commentary node will not stop music or sounds.
- On all Valve games, the co-founder, Gabe Newell, will make the introductory commentary, which usually consists of an explanation of how to control the nodes. At the end of some games, he will make the final commentary.
 List of appearances