ActionScript 3.0 :: Predicting The External SWF Content?

I am importing an SWF as library at runtime

Code:

private function loadDeck(str:String)
{
var ldr:Loader = new Loader();
var request:URLRequest = new URLRequest(str);

[code]....

Then I can access all SWF linkages directly, as I added the SWF library to the app-domain.But...! When I instantiate a new object from the SWF library, the compiler does not know the new Class, and tells me it is not a known object, obviously.I fixed this problem deselecting "Strict Mode" from the FLA publish settings, but which is the best way to declare the exhistance of a certain class of an external SWF before it is loaded?