Returns TRUE if the filename exists and is a symbolic link.
注: 此函數的結果會被快取。詳細資訊請參考 clearstatcache()。
提示: As of PHP 5.0.0 this function can also be used with some URL wrappers. Refer to 附錄 L for a listing of which wrappers support stat() family of functionality.
See also is_dir(), is_file(), and readlink().