ActionScript: The Definitive Guide

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 programmer’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. 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 ...