If I have rolled my own RSL, and I want to use it in my pure as3 apps, is there documentation or an example of how to do this?
Or do I need to traverse the flex source code to figure out what adobe's engineers have done?
This is a very tricky one, with lots to go into I'm afraid. Some pointers:
To get a class from an externally loaded SWF use the getDefinition method on an application domain e.g.
public function loadHandler(evt:Event):void
{
var loaderInfo:LoaderInfo = evt.target as LoaderInfo;
var clazz:Class = loaderInfo.applicationDomain.getDefinition("your.external.class");
}
This will give you the class definition if you know the name of the class you want.
To 'join' class domains into each other (so applications can compile against a swc, but not include the classes and load them externally) you need to specify a loaderContext of the same security domain.
var loader:Loader = new Loader();
var context:LoaderContext = new LoaderContext();
context.applicationDomain = ApplicationDomain.currentDomain;
loader.load(new URLRequest("library.swf"), context);
The third pointer I can give you is the compiler option "-external-library-path", use this to specify a list of swc's to compile time check against, but not include (resulting in a lower filesize).
mxmlc -source-path="dir/src" -external-library-path="dir/lib/framework.swc" --main.swf
Sorry I couldn't elaborate more, it's a very expansive topic, hope this gets you started....