Is this html?

This is a snipet of code that I've got, its part of some integrated way of doing xml/xsl stuff with php, but I don't fully understand it, and it would be useful:

<td class="listtd"><xsl:value-of select="id" /></td>

What I'm most in want of knowing about at present is the class= part, if you know whether it is normal html, a part of the xml/xsl stuff or something else I'd like to know. I suspected that it was something put in for latter reference somewhere but I can't find a later reference, of course that could be because that section is not complete yet. Your thoughts are appreciated.

class would be referring to css.. you define what styles you want for your td tags in the header like this

td{blah; blah;}
td.listtd{blah; blah;}

and then you can call that specific style set by using <td class="listid"> make sense?

here is a link to hopefully shed some light on the xsl part: http://www.w3.org/TR/xslt20/#value-of
it is not html but using an xsl parser it could very well generate html. as far as how to use an xsl parser i have no clue, i just know of them.