# MovieClip.setMask()

#### Availability

Flash Player 6.

#### Usage

`my_mc``.setMask (``mask_mc``)`

#### Parameters

`my_mc` The instance name of a movie clip to be masked.

`mask_mc` The instance name of a movie clip to be a mask.

#### Returns

Nothing.

#### Description

Method; makes the movie clip in the parameter `mask_mc` into a mask that reveals the movie clip specified by the `my_mc` parameter.

This method allows multiple-frame movie clips with complex, multilayered content to act as masks. You can shut masks on and off at runtime. However, you can't use the same mask for multiple maskees (which is possible by using mask layers). If you have device fonts in a masked movie clip, they are drawn but not masked. You can't set a movie clip to be its own mask, for example `my_mc.setMask(my_mc)`.

If you create a mask layer that contains a movie clip, and then apply the `setMask()` method to it, the `setMask()` call takes priority and this is not reversible. For example, you could have a movie clip in a mask layer called `UIMask` that masks another layer containing another movie clip called `UIMaskee`. If, as the movie plays, you call `UIMask.setMask(UIMaskee)`, from that point on, `UIMask` is masked by `UIMaskee`.

To cancel a mask created with ActionScript, pass the value `null` to the `setMask()` method. The following code cancels the mask without affecting the mask layer in the Timeline.

    UIMask.setMask(null);

#### Example

The following sample code uses the movie clip `circleMask_mc` to mask the movie clip `theMaskee_mc`.

    theMaskee_mc.setMask(circleMask_mc);