Built-in Movie Clip Properties

Unlike generic objects of the Object class, which have few built-in properties, each movie clip comes equipped with a slew of built-in properties. These properties describe, and can be used to modify, the clip's physical features. They are fundamental tools in the ActionScript developer's toolkit.

All built-in movie clip property names begin with an underscore, which sets them apart from user-defined or custom properties. Built-in properties take the format:

_ property

Built-in property names should be written in lowercase. However, because identifiers are case insensitive in ActionScript, it is possible -- though not good form -- to capitalize property names.

We're not going to go into heavy descriptions of the built-in properties right now; that information is listed in Part III, "Language Reference". However, to get us thinking about properties and what they offer, Table 13-1 provides a list of the built-in movie clip properties and basic descriptions of their functions.

Table 13-1. The Built-in Movie Clip Properties

Property Name	Property Description
`_alpha`	Transparency level
`_currentframe`	Position of the playhead
`_droptarget`	Path to the clip or movie on which a dragged clip was dropped
`_framesloaded`	Number of frames downloaded
`_height`	Physical height, in pixels (of instance, not original symbol)
`_name`	Clip's identifier, returned as a string
`_ parent`	Object reference to the timeline containing this clip
`_rotation`	Angle of rotation (in degrees)
`_target`	Full path to the clip, in slash notation
`_totalframes`	Number of frames in the timeline
`_url`	Network location of swf
`_visible`	Boolean indicating whether movie clip is displayed
`_width`	Physical width, in pixels (of instance, not original symbol)
`_x`	Horizontal position, in pixels, from the left of the Stage
`_xmouse`	Horizontal location of the mouse pointer in the clip's coordinate space
`_xscale`	Horizontal size, as a percentage of the original symbol (or main timeline for movies)
`_ y`	Vertical position, in pixels, from the top of the Stage
`_ ymouse`	Vertical location of the mouse pointer in the clip's coordinate space
`_ yscale`	Vertical size, as a percentage of the original symbol (or main timeline for movies)

There's no direct color property attached to instances or main movies. Instead of controlling color through a property, we must use the Color class to create an object that is used to control the color of a clip. The methods of a Color object let us set or examine the RGB values and transformations of a particular clip. To learn the specific details, see the Reference 20.22 in Part III, "Language Reference".