X12 EDI, been there earned the badge, both on the generating and receiving sides. 837, 834, 835 and others in health care - fun! Positional format, with situational meaning... really it is a fascinating format.
i wrote the X12 EDI stuff for a major clearwater distributor... also wrote the ACH stuff that dumped someone a file and their job was to upload it via SFTP to the bank. so many badges.