How to pass a variable to an externally loaded swf


I’m having trouble finding information of this topic that isn’t for AS2. If someone could point me in the right direction I would really appreciate it.

In my main swf I set a string variable containing the name of the xml file that needs to load into an externally loaded swf file. How do I then pass that information into the external swf once it’s loaded into the main swf?

Thanks for any help.