a types:</p>

<ol>
<li>
CSS style sheets 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 contin