Highlight a keyword without breaking tag

gistfile1.php

// $value is the original string
// $keyword is the searching keyword
function highlight($value, $keyword) {        
    try {
        $dom = new DomDocument();
        @$dom->loadHtml($value);
        $xpath	  = new DomXpath($dom);
        $upper	  = strtoupper(addslashes($keyword));
        $lower	  = strtolower(addslashes($keyword));
        // Support i-case sensitive using translate method provided by XPath 1.0
        $query	  = '//*[contains(translate(., "' . $upper . '", "' . $lower . '"), "' . $lower . '")]';
        $elements = $xpath->query($query);
    
        foreach ($elements as $element) {
            foreach ($element->childNodes as $child) {
                if (!$child instanceof DomText) {
                    continue;
                }
                $fragment = $dom->createDocumentFragment();
                $text	  = $child->textContent;
                while (($pos = stripos($text, $keyword)) !== false) {
                    $fragment->appendChild(new DomText(substr($text, 0, $pos)));
                    $word	   = substr($text, $pos, strlen($keyword));
    
                    // Create a SPAN element
                    $highlight = $dom->createElement('span');
                    $highlight->appendChild(new DomText($word));
                    $highlight->setAttribute('class', 'coreFiltersHighlight');
                    $fragment->appendChild($highlight);
                    $text = substr($text, $pos + strlen($keyword));
                }
                if (!empty($text)) {
                    $fragment->appendChild(new DomText($text));
                }
                // Replace the text node element with the new one that contains the SPAN tag
                $element->replaceChild($fragment, $child);
            }
        }
        return $dom->saveXml($dom->getElementsByTagName('body')->item(0)->firstChild);
    } catch (Exception $ex) {
        return preg_replace('/(?![^<>]*>)' . preg_quote($keyword, '/') . '/i', '<span class="highlight">' . $keyword . '</span>', $value);
    }
}