Missing fieldset, legend, optgroup at XHTML-Print

Dear all,

Can someone tell me why the following tags are missing at XHTML-Print?

  * fieldset
  * legend
  * optgroup

Maybe a remaining bad-miss inherited from XHTML-Basic?

I think there is no reason why these tags had been removed. I still expect 
those tags to be re-included in a revised version of XHTML-Basic.

Thank you.

Vicente Luque Centeno
Dep. Ingeniería Telemática
Universidad Carlos III de Madrid
http://www.it.uc3m.es/vlc