XHTML Transitional DTD and <td> tags

According to the XHTML Transitional DTD on the w3c site, <td> tags can only
have pixel widths applied and not percents, as indicated below by the
%Pixels.  Is this an error? Should the DTD show %Length instead, as in the
HTML 4 Transitional DTD, or has this been changed in the XHTML DTD?  If this
is correct, can you please tell me why percentages are no longer valid??

Also, I checked two XHTML books (Beginning XHTML by WROX and HTML & XHTML
The Definitive Guide by O'Reilly), and both books confirm that pixel and
percentage widths can be used in the <td> tag.

Here is the portion of the DTD that I am referring to:

<!ATTLIST td
  %attrs;
  abbr        %Text;         #IMPLIED
  axis        CDATA          #IMPLIED
  headers     IDREFS         #IMPLIED
  scope       %Scope;        #IMPLIED
  rowspan     %Number;       "1"
  colspan     %Number;       "1"
  %cellhalign;
  %cellvalign;
  nowrap      (nowrap)       #IMPLIED
  bgcolor     %Color;        #IMPLIED
  width       %Pixels;       #IMPLIED
  height      %Pixels;       #IMPLIED
  >


Thanks!!
Laurel Oglesby
Web Developer
Rivio, Inc.