HTML_Definition_List_Example.php

<?php

$xml = <<<XML
<dl>
<dt>Cascading Style Sheets</dt>
<dd><p>Style sheets are used to provide presentational suggestions.</p>
<p>Documents structured using XML or HTML are able to make use of them.</p></dd>
<dt>Content Management</dt>
<dd>The process of collecting, managing and publishing content to various media.</dd>
<dd>A dirty job that no one wants.</dd>
</dl> 
XML;

$defs = array();

$a = new DOMDocument();
$a->loadXML($xml);
$xpath = new DOMXPath($a);
$dl = $xpath->query('/dl')->item(0);
foreach($dl->childNodes as $child) {
    $curr = $child->textContent;
    if ($child->tagName == 'dt') {
        $term = $curr;
    }
    if ($child->tagName == 'dd') {
    	# it's a definition for the last 'dt' we saw
        if (isset($defs[$term])) {
        	if (is_array($defs[$term])) {
        		$defs[$term][] = $curr;
        	} else {
        		$prev = $defs[$term];
        		$defs[$term] = array($prev, $curr);
        	}
        } else {
            $defs[$term] = $curr;
        }
    }
}

var_dump($defs);