bidi

Hi Fredrik, David, all,

Sorry I had to leave at the top of the hour. 
I don't know what was decided, but removing dir from source/target may be quite helpful at the implementation level as it become a
lot easier to get inherit directly from the unit. So I wouldn't see any problem going in that direction.

That doesn't answer the basic issue of directionality at the inline-level (values for <pc>/<sc>, using control chars or not, etc.)
but it eliminates the question from the segmentation modification.

BTW: should <ec> have dir too? (when isolated)

Cheers,
-yves