Mac OS X seems to be a little confused as to what it should use to open files. It seems to be able to use both the antiquated 8.3 naming scheme to tell it what app to use, and it also is able to use the resource fork when there's no file name extension. Which does OS X really use, or does it use both?

For example, my Documents folder is a hodgepodge of files, some using the 8.3 naming scheme, others using the classic naming scheme. And they all still open. I love it, but it is rather confusing. Which does OS X prefer?