Странное условие и др. вопросы

//
// Convert a series of smilies to images
//
function do_smilies($text)
{
    global $smiley_text, $smiley_img;

    $text = ' '.$text.' ';

    $num_smilies = count($smiley_text);
    for ($i = 0; $i < $num_smilies; ++$i)
        $text = preg_replace("#(?<=.\W|\W.|^\W)".preg_quote($smiley_text[$i], '#')."(?=.\W|\W.|\W$)#m", '$1<img src="img/smilies/'.$smiley_img[$i].'" width="15" height="15" alt="'.substr($smiley_img[$i], 0, strrpos($smiley_img[$i], '.')).'" />$2', $text);

    return substr($text, 1, -1);
}