Basic div pair highlighter

pairs.php

<?php

$contents = htmlspecialchars(@$_POST['contents']);

if (!$contents) { ?>
<form method="post">
    <textarea name="contents"></textarea>
    <br>
    <input type="submit">
</form>
<?php
    exit;
}

$processed = '';
$divs = array();
$total = 0;
$current = 0;

while (preg_match('@(&lt;/?div)@i',$contents,$match)) {
    $div = $match[1];
    
    if ($div{4} == '/') {
        $level = count($divs);
        $current = array_pop($divs);
    }
    else {
        $total++;
        $current = $total;
        $divs []= $current;
        $level = count($divs);
    }
    
    $new = str_replace('div','<span class="div-encloser div-pair-' . $current . ' div-level-' . $level . '">div</span>',$div);
    $contents = preg_replace('@' . preg_quote($div) . '@',$new,$contents,1);
}

?>
<script type="text/javascript" src="js/jquery-1.4.3.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
    $('span').bind('click',function(){
        var $this = $(this),
        classes = $this.attr('class'),
        pair = classes.replace(/.*?(div-pair-[^ ]*).*/ig,'$1'),
        level = classes.replace(/.*?(div-level-[^ ]*).*/ig,'$1');
        
        $('.div-encloser').removeClass('active-pair').removeClass('active-level');
        $('.' + pair).addClass('active-pair');
        $('.' + level).addClass('active-level');
    })
});
</script>
<style type="text/css">
span
{font-weight:bold;}

.active-pair
{color:#f33;}

.active-level
{background-color:#ccc;}
</style>
<pre><?php echo $contents ?></pre>