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My decorator implementation has two requirements that distinguish it from the classic pattern:
1) Decorators add new behavior to the class it wraps (while also modifying existing behavior)
2) New behavior must be accessible
2) A decorated object can be undecorated

This led to some interesting challenges such as,
A) Once an object is decorated several times, how to check if the objects implements an interface implemented by a decorator. (I found no way to modify an object’s type at runtime)
B) How to un-decorate an object that is decorated

I solved these challenges by adding a undecorate, retrieveDecorator, and static decorate functions to each decorated/decorator object.

In this way I can dynamically decorate/undecorate an object and therefore dynamically add and remove behavior to an object. I can also access added dynamic behavior by calling retrieveDecorator, assigning its return value to a local variable and invoking

An example of using this is:

var decorated:DecoratedObject = new ConcreteDecoratedObject();
decorated = DecA.decorate( decorated ); //adds IDecA behavior
decorated = DecB.decorate( decorated ); //adds IDecB behavior

trace( decorated is IDecA ); // RETURNS FALSE
trace( decorated is IDecB ); // RETURNS TRUE

// to access IDecA behavior, I must do this
var decA:IDecA = decorated.retreiveDecorator( IDecA ) as IDecA;
if( decA != null )
{
// access decA behavior here
}