When using strip_tags() with the optional conversion 
param, it still strips round brackets "()" from the input 
string.
Example:
<?php
$allowed = "<a>";
$tag = "<a href=\"$PHP_SELF\" "; 
$tag .= "onClick=\"alert('Hello')\">click</a>";
printf("%s", strip_tags($tag, $allowed));
?>
results in
<a href="whatever.php" onCLick="alert'Hello'">click</a>
missing brackets---------------------^-----^

and leaves the <a> Tag unuseable.