Link Back?

Hi. 

Just wanted to know what is the status for link back from XRD2 to XRD1. 

I have seen a lot of discussion for forward linking XRD1 to XRD2, 
but I am not so sure about XRD2 back to XRD1. 

Presumably, we can just define <rel> that signifies the link back, 
but have we defined or discussed it? 

Regards, 

=nat