Additional Timelines can also be used in the form of SWF files placed in levels. Every Flash document has a main Timeline located at level 0 in Flash Player, which is referred to as the Base Level. The Base Level determines the size, frame rate and background color for the entire file. Each document loaded into a level of Flash Player has its own Timeline. So here again, is a way to use multiple Timelines, all playing at the same time, within a single file.
Each level can be addressed in an absolute fashion, which is how you achieve some control of each Timeline. Level 0 is addressed as _level0, level 1 as _level1, and so on. Only level 0 exists until content is loaded into other levels using the loadMovie action. This action loads other Flash SWF files into Flash Player at the designated level.
If you load documents into levels above level 0, the documents stack on top of one another like drawings on transparent paper; when there is no content on the Stage, you can see through to the content on lower levels. If you load a document into level 0, it replaces the main Timeline.
Once content has been loaded into a level, you treat the level just like any other movie clip object. A SWF file or image loaded into a movie clip inherits the position, rotation, and scale properties of the movie clip. You can also use the target path of the movie clip to target the loaded SWF file.
This is pretty slick!
There is however, a difference between _root and _level0. In movies in which level 0 is the only level in a movie, these keywords do refer to the same object. However, _root within a movie loaded into level 1 would refer to _level1.
For more information on the target paths and flash levels, view the relevant Flash tutorials on my web site.