[XBL] @extends and multiple inheritance

In reference to [1] specifically @extends: It seems somewhat clear that 
multiple URIs and therefore multiple inheritance is disallowed.  It only 
states "the URI of a binding", could be helpful to clearly state that only 
1 URI is allowed.

But by reading [2] it seems like multiple inheritance can sort of be 
achieved by using implicit bindings as described in "4.7 Binding 
Inheritance".  Any reason not to support multiple inheritance explicitly 
by allowing multiple base URIs to extend (or some such appropriate 
mechanism in <binding>)?

Regards,
Steve Speicher

[1] http://www.w3.org/TR/2006/WD-xbl-20060907/#the-binding
[2] http://www.w3.org/TR/2006/WD-xbl-20060907/#binding1