ATAG 2.0 - A.3.1.2 Avoiding Content Keyboard Traps

In A.3.1.2 (Avoiding Content Keyboard Traps) we say:

"If an editing view (e.g., WYSIWYG view) renders web content, then a 
documented keyboard command is provided that will always restore 
keyboard focus to a known location (e.g., the menus)
AND
a documented keyboard command is provided that will always move keyboard 
focus to the subsequent element that can receive focus."


ISSUE:
I like the first requirement but I'm wondering if the second is always 
possible. For example if the authoring tool is using a browser component 
for the rendering and there is an AJAX control grabbing the TAB presses 
it might not be possible to move focus to the subsequent element with 
that typical control.

Any thoughts?

Cheers,
Jan