When you load a SWF file, you can set the context parameter of the load() method of the Loader object that is used to load the file. This parameter takes a LoaderContext object. When you set the securityDomain property of this LoaderContext object to Security.currentDomain, Flash Player checks for a cross-domain policy file on the server of the loaded SWF file. If there is a cross-domain policy file, and it grants access to the domain of the loading SWF file, you can load the SWF file as imported media. In this way, the loading file can get access to objects in the library of the SWF file.

An alternative way for a SWF file to access classes in loaded SWF files from a different security sandbox is to have the loaded SWF file call the Security.allowDomain() method to grant access to the domain of the calling SWF file. You can add the call to the Security.allowDomain() method to the constructor method of the main class of the loaded SWF file, and then have the loading SWF file add an event listener to respond to the init event dispatched by the contentLoaderInfo property of the Loader object. When this event is dispatched, the loaded SWF file has called the Security.allowDomain() method in the constructor method, and classes in the loaded SWF file are available to the loading SWF file. The loading SWF file can retrieve classes from the loaded SWF file by calling Loader.contentLoaderInfo.applicationDomain.getDefinition().