Supprimer les balise dans textarea

<?php
 
//include "geshi/geshi.php"; 
 
function previewDiv($texte){
     
    $texte = htmlentities($texte);
    $texte = preg_replace_callback("#<code=(.+)>(.*)<\/code>#siU", create_function('$matches', 'return code($matches[2], $matches[1]);'), $texte);
    $texte = preg_replace("/<gras>(.*)<\/gras>/siU", "<span class=\"gras\">$1</span>", $texte);
    $texte = preg_replace("/<italique>(.*)<\/italique>/siU", "<span class=\"italique\">$1</span>", $texte);
    $texte = preg_replace("/<souligne>(.*)<\/souligne>/siU", "<span class=\"souligne\">$1</span>", $texte);
    $texte = preg_replace("#<color=(red|green|purple|blue|yellow)>(.*)</color>#siU", "<span style=\"color:$1\">$2</span>", $texte);
    $texte = preg_replace("/<nav>(.*)<\/nav>/siU", "$1", $texte);
    $texte = mynl2br($texte);   
    return($texte);
}
 
function code($source, $language){
     
    $source = html_entity_decode($source);
    $code = new GeSHi($source, $language); 
    $parse = $code->parse_code();
    $resultat = '<div>Code : '.$language.'<br/>'.$parse.'</div>';
     
    return ($resultat);
     
}
 
 
function mynl2br($text) {
   return strtr($text, array("\r\n" => '<br />', "\r" => '<br />', "\n" => '<br />'));
}
 
 
?>