2.1 a-d: Link Recognition by Reserved Attribute?

The ERB schedule calls for voting on these Feb. 19th.
I've take the liberty of grouping a few here that seem totally related.

2.1.a Should we allow link recognition via a reserved attribute? 

2.1.b If so, should we generalize this and say that it's an AF? 

2.1.c If so, should we provide an introduction to AF's? 

2.1.d If we allow such recognition, what should the attribute be, and 
      what should be the values for each element type we define? 

Cheers, Tim Bray
tbray@textuality.com http://www.textuality.com/ +1-604-708-9592