Question Regarding Tab Completion in Bash

I noticed something with the bash shell recently (might be old and just never really noticed it before) If I have 3 files in a directory, such as follows: file_1.tar file_2.tar file_3.tar.gz If I type 'gzip -df file' and then hit TAB to start path completion, it knows to select the file_3.tar.gz because it is the only file with a *.gz extension. (I am assuming) Just curious where this new functionality was implemented. Is this done to bash itself or via some other mechanism? I am looking to do something like this for some code I am writing... Thx, cc