strtotime -- 将任何英文文本的日期时间描述解析为 Unix 时间戳

echo    strtotime("+1    day"),    "/n";
echo    strtotime("+1    week"),    "/n";

strtotime("+1    day    ".$day);
strtotime("2008-01-31    +1    month");
strtotime($day."    +1    day");