+1, always thought it was an IBM standard, move with TAB and commit the form with ENTER.

Correct. I found a PDF of the Operator's Guide. See https://news.ycombinator.com/item?id=48028227

That's exactly my memory too, using a tab was second nature and it irked me when I went to gui apps with a mouse and the tab order was wrong, mainly with visual basic apps.

It's been ages since I used an IBM green screen but I seem to recall that in our application Tab did move between fields, but I think there were also function keys reserved for this purpose.

I wonder about the midrange systems. I never used AS/400's, but I know they have the concept of a a "Field Exit" key separate from <ENTER>.