Tohle se tyka prevazne jednoducheho parseru v PHP, jde hlavne o regularni vyrazy
http://www.regexp.cz/
<?php
$file[$a] = ereg_replace("(\[)[b](\])+([-A-Za-z0-9:\./_\?&;=\+\* ]*)(\[/)[b](\])", "<b>\\3\" </b>", $file[$a]);
?>
http://www.php.net/manual/en/function.eregi-replac e.php
