PHP to closes any open LTR/RTL unicode controls

function bidi_cleanup($str){
    # Closes all embedded RTL and LTR unicode formatting blocks in a string so that
    # it can be used inside another without controlling its direction.
    # More info: http://www.iamcal.com/understanding-bidirectional-text/
    #
    # LRE - U+202A - 0xE2 0x80 0xAA
    # RLE - U+202B - 0xE2 0x80 0xAB
    # LRO - U+202D - 0xE2 0x80 0xAD
    # RLO - U+202E - 0xE2 0x80 0xAE
    #
    # PDF - U+202C - 0xE2 0x80 0xAC
    #
    $explicits  = '\xE2\x80\xAA|\xE2\x80\xAB|\xE2\x80\xAD|\xE2\x80\xAE';
    $pdf        = '\xE2\x80\xAC';

    $stack = 0;
    $str = preg_replace_callback("!(?<explicits>$explicits)|(?<pdf>$pdf)!", function($match) use (&$stack) {
        if (isset($match['explicits']) && $match['explicits']) {
            $stack++;
        } else {
            if ($stack)
                $stack--;
            else
                return '';
        }
        return $match[0];
    }, $str);
    for ($i=0; $i<$stack; $i++){
        $str .= "\xE2\x80\xAC";
    }
    return $str;
}