There seems to be several choices:
    a)  require browsers to differentiate each of the physical
        styles (B, I, U, TT and S)
    b)  introduce <em1>, <em2>, ...<em4>
    c)  Use Bryan Oakley's FACE idea and require browsers
        to differentiate a small set of style names
Right now, the simplest seems to use (a) and encourage browsers
to comply with differentiating the small set of existing physical styles.
Dave Raggett