Represents the position of the mouse event collision detection formula.
You can also set the value.
This property is valid only when the Layer.hitType property is htMask, and a mouse message will be received if the mask (opacity) image value is greater than or equal to the value specified in this property.
Specify 0 to receive all mouse messages.
If you specify 256, all mouse messages will not be received.
The initial state is 16.