$patterns = array ('/(19|20)(\d{2})-(\d{1,2})-(\d{1,2})/',  '/^\s*{(\w+)}\s*=/');

$replace = array ('\3/\4/\1\2', '$\1 =');                       

echo preg_replace($patterns, $replace, '{startDate} = 1999-5-27'); 

此例中$patern和$replace是数据，怎么理解呢？求高手讲讲。谢谢！