 for XHTML should use lower case element and
attribute names.</li>


<li>In tables, the tbody element will be inferred by the parser of an
HTML user agent, but not by the parser of an XML user agent. Therefore
you should always explicitely add a tbody element if it is referred to
in a CSS selector.</li>

<li>Within the XHTML name space, user agents are expected to
recognize the "id" attribute as an attribute of type ID.
Therefore, style sheets should be able to continue using the
shorthand "#" selector synt