Tweener Documentation
AS2 and AS3.
Tweener.registerSpecialPropertyModifier(name:String, modifierFunction:Function, getFunction:Function);
name:Number — The name of the new special property modifier you want to create. This name cannot conflict with the name of any existing tweening parameter, and it's recommended that you do not use the name of any special property already existing as this would overwrite them.
modifierFunction:Function — A function that receives one object, which is the parameter passed to this special property. It must return an array listing the name of the property that will have a modifier act on it, plus any additional parameters needed.
getFunction:Function — A function that acts a bit like a transition function; it receives four parameters: the beginning value of a property, the target value, the current time (from 0 to 1) in the transition, and one additional parameter (an array) containing the original objects as definied by the modifierFunction.
Creates and registers a new special property modifier. This acts like a proxy modifier, which acts on the top of other existing properties; that is, a new modifier is not a special property in itself, but rather, acts on other properties being tweened on the same tweening.
Nothing.
This is a complex topic. See the caurina/transitions/properties/CurveModifiers.as file for an example based on the _bezier special property modifier.