php Regex報錯，

php Regex報錯，高手請進。
$str = preg_replace("/(?]*)(茶葉)(?!\"|<\/a>)/sui", '茶葉', $str, 5);

報錯如下：
Warning: preg_replace() [function.preg-replace]: Compilation failed: lookbehind assertion is not fixed length at offset 10 in D:\AppServ\www\Template\test.php on line 28


------解決方案--------------------
試試

PHP code

        $html = <<中國茶葉這兒是中國茶葉大觀的連結。這兒是茶葉的現有連結html;        echo preg_replace('#(?=[^>]*(?=<(?!/a>)|$))茶葉#','\0',$html);    }
