undo html

[vividona]

I am using htmlspecialchars() function to change some of html tags

Now I need to highlight my php codes.

[PHP]public function bb_php($string)
    {
        string = str_replace ( '&', '&', $string );
        $string = str_replace ( ''', '', $string );
        $string = str_replace ( '"', '', $string );
        $string = str_replace ( '&lt;', '<', $string );
        $string = str_replace ( '&gt;', '>', $string );
        
        $match = array('#\[php\](.*?)\[\/php\]#se');
        $replace = array("'<div>'.highlight_string(stripslashes('$1'), true).'</div>'");
        
        return preg_replace($match, $replace, $string);
    } 

This code undo html tags from the whole page.
I need to remove it only from php codes[/PHP]