How can I replace strings NOT within a link tag?

Question

I am working on this PHP function. The idea is to wrap certain words occuring in a string into certain tags (both, words and tags, given in an array). It works OK!, but when

Answer 1

Use the DOM and only modify text nodes:

$s = "foo foo lorem bar ipsum foo. bar not a test";
echo htmlentities($s) . '
';

$d = new DOMDocument;
$d->loadHTML($s);

$x = new DOMXPath($d);
$t = $x->evaluate("//text()");

$wrap = array(
    'foo' => 'h1',
    'bar' => 'h2'
);

$preg_find = '/\b(' . implode('|', array_keys($wrap)) . ')\b/';

foreach($t as $textNode) {
    if( $textNode->parentNode->tagName == "a" ) {
        continue;
    }

    $sections = preg_split( $preg_find, $textNode->nodeValue, null, PREG_SPLIT_DELIM_CAPTURE);

    $parentNode = $textNode->parentNode;

    foreach($sections as $section) {  
        if( !isset($wrap[$section]) ) {
            $parentNode->insertBefore( $d->createTextNode($section), $textNode );
            continue;
        }

        $tagName = $wrap[$section];
        $parentNode->insertBefore( $d->createElement( $tagName, $section ), $textNode );
    }

    $parentNode->removeChild( $textNode );
}

echo htmlentities($d->saveHTML());

Edited to replace DOMText with DOMText and DOMElement as necessary.