what file extension do i use with nskeyedarchiver

I am writing an app that u开发者_JS百科ses NSKeyedArchiver to save its data. Should my file be ishotTrack.plist or ishotTrack.arch?

The archives created with NSKeyedArchiver are binary property lists, so it makes sense to use plist file name extension. On the other hand they aren't human-readable, so opening the plist won't help anybody much.