Can't figure out flow (workflow)

To start off, I did search, either most of these posts were completely ignored, were told to search… Or didn’t actually answer my question as well as I had hoped, I also can’t find any documentation (Good job?) and the only blog post showing off workflows has had all its screenshots deleted so that is about as helpful as the documentation.

Question is rather simple, how do I make it match to files that have extension .xyz? I tried .xyz, I tried /.xyz/ and I have tried /.xyz/, all 3 did not seem to work at all, unfortunately. So it would be great if I could get a push in the right direction. I have set up multiple workflows already based on the folder they are in, but that just doesn’t cut it no more.

Thanks in advance!