xlink:fromID , xlink:toID

Presently one can of course assign an xlink:label attribute to the 
source or target of a link. However, in order to have the option to 
ensure that the source and/or target of a particular xlink was unique, I 
believe having such attributes as xlink:fromID and xlink:toID used in 
conjunction with xml:id (or with an attribute of type ID) could meet 
that demand

thank you,
Brett Zamir