Is there any way to determine which movie an ExternalInterface.call came from?

On my page, I'm going to embed multiple Flash files that use ExternalInterface to communicate ba开发者_StackOverflowck to the page. When the page receives the ExternalInterface calls, is there any built-in way to determine which swf the call came from?

I don't mind giving each movie a guid FlashVar and attaching that to each ExternalInterface call, but I don't want to duplicate more tested functionality.

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What you're think is really your only solution. Passing unique IDs to the SWFs is the only way.