I didn't even know that was possible! Nice improvement indeed.

This is still a bit obscure to me... how about:
Add an event callback forwarder that will make this object emit an event whenever another object ($new_obj) emits it. The event is said to be forwarded from $new_obj to this object.

So confusing! So the event is unaffected, but it can be intercepted? How about:

$new_obj still emits the original event. Whether this object emits the forwarded event before or after $new_obj can be controlled by the $priority parameter (see below).
In order to prevent $new_obj from emitting the initial event, register the forwarder using the @Efl.Callback_Priority_Before and then stop further propagation of the event by ... (explain briefly how you do that, because I don't know. Add link to where that is explained. It should be https://www.enlightenment.org/develop/guides/c/core/events.md but that part is missing).

Wow, I didn't know @cref. What does it do?
Also, it needs @in.

Do not change the name of the thing! We have been calling it "event forwarder", so keep calling it "event forwarder" (not "redirection handler").

I would call this original_obj, and the comment should be [[The object which emits the initial event]]

Change my previous comments accordingly if you call this parameter something other than new_obj.

I am removing completely the reference to event interception as this is confusing and unrelated to forwarder (all events can be blocked from propagating there event further with efl_event_callback_stop).

To my understanding @cref is a const pointer to an object that the caller keep control of after the call. I would for example not expect this call to keep a reference somewhere to desc once the call is done. Arguably, this is one of this things where onle @q66 and @felipealmeida will be able to give the exact definition.

It also imply @in as const pointer can not be modified and so can't be an out.