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About movie clip hierarchy

When you place a movie clip instance on another movie clip's Timeline, the placed movie clip is the child and the other movie clip is the parent. The parent instance contains the child instance. The root Timeline for each level is the parent of all the movie clips on its level, and because it is the topmost Timeline, it has no parent.

The parent-child relationships of movie clips are hierarchical. To understand this hierarchy, consider the hierarchy on a computer: the hard drive has a root directory (or folder) and subdirectories. The root directory is analogous to the main Timeline of a Flash movie: it is the parent of everything else. The subdirectories are analogous to movie clips.

You can use the movie clip hierarchy in Flash to organize related visual objects. Any change you make to a parent movie clip is also performed on its children.

For example, you could create a Flash movie of a car that moves across the Stage. You could use a movie clip symbol to represent the car and set up a motion tween to move it across the Stage.

A motion tween moves the car movie clip on the main Timeline.

To add wheels that rotate, you create a movie clip for a car wheel, and create two instances of this movie clip, named `frontWheel` and `backWheel`. Then you place the wheels on the car movie clip's Timeline—not on the main Timeline. As children of `car`, `frontWheel` and `backWheel` are affected by any changes made to `car`; they will move with the car as it tweens across the Stage.

The wheel instances are placed on the Timeline of the car parent movie clip.

To make both wheel instances spin, you set up a motion tween that rotates the wheel symbol. Even after you change `frontWheel` and `backWheel`, they continue to be affected by the tween on their parent movie clip, `car`; the wheels spin, but they also move with the parent movie clip `car` across the Stage.

The wheel symbol in symbol-editing mode