Is there any equivalent to IE conditional comment for chrome and safari?

Question

I am wondering if there is any thing which works like ie conditional comment for webkit.

I want to change width.

For example,

';
}
if ($safari) {
echo '';
}

?>




    

    you are not using Internet Explorer
';
    }
    if ($msie) { // IE?
    echo '
you are using Internet Explorer
';
    }
    ?>

    

From Chrome conditional comments