Choice Links and End Links are typically the name of a scene that you'd like the engine to load. There's a few secret alternatives:

• Register tags : By using [r:variableName] instead of a traditional name, the engine will attempt to find a stored value to use as a link. By setting a stored value to the name of a scene, you can define and re-define the behavior of a link on-the-fly as the player works through your game. Just be careful with your logic–if a stored value has not been set when the link is activated, this could result in no scene being found, which will cause the dialog to end.
• Moment Links : In addition to choosing a scene name, you can also specify the specific moment you'd like to load. Simply type the scene name, followed by a colon and moment. For example, “intro:3” would jump to a scene named intro and a moment within the scene named 3. This feature is particularly useful for circular dialog, where the player is expected to choose an option, read the resulting dialog, and then return back to the options screen again.
• Rooms : GameMaker games frequently use rooms to load and unload sets of game objects. You can use the name of a room instead of a scene and GameMaker will change to that room rather than switching to a scene. Bear in mind, the showDialog object is not Persistent by default, so you may need to change this if you need the Show object to follow the room. See GameMaker's Object Editor page for details about objects and persistence.