Note that the unknown attributes are not eliminated in transmission;
they're there for the client to act upon if it has some instructions
for dealing with them. If your client had that capacity, you could
use unknown atts to enrich the semantics of the existing HTML
markup (<EM role=vegetable>) for such things as searching, without
impairing the ability of other clients to render the text.
Regards,
-- Terry Allen (terry@ora.com) Editor, Digital Media Group O'Reilly & Associates, Inc. Sebastopol, Calif., 95472