Xantrax says it's "generator support"
A key feature enhancement is ‘Generator Support Mode’ which enables the Freedom SW to supplement a generator¹ when AC loads exceed the generator’s capacity. The new generation models also feature improved AC transfer/AC input detection time, providing the ability to transfer AC loads to batteries in less than 10 milliseconds when the incoming grid or generator power is lost."
I guess it sounds like you are right and maybe you can't dial back the ac input like the magnum or victron.
http://www.xantrex.com/power-products/inverter-chargers/freedom-sw-12v_newgen.aspx