I am currently redesigning a functionality where you can mark an arbitrary content object through a behavior as unavailable. An unavailable object would show up with a standard/custom text "I am available" or with a redirect to a configurable URL (configured through the behavior).
The current implementation assigns a marker interface for unavailable object (which is fine).
Marking a folder as unavailable make also all subcontent unavailable.
The question is how to hook into the traversal in order to intercept each component of a traversal for performing the check "are you marked as unavailable".
__bobo_traverse__ is not an option because this functionality should work without touch any other code.