AdamFowler_ITI get impressed when I have to fill out a PDF that has actual typable text fields, and they're all in order so when I have to tab from field to field, it jumps correctly.
I didn't get impressed today.
Pseudonymous 
This has been a bugaboo I've had a solution to for a long time: Make the default letting the user system follow the text direction. If the publisher wants to, give them the capability to define a different Tab sequence. 
Poof! Problem solved. 
Put me personally in charge of tech standards, damnit. 