Returns TRUE if the filename exists and is writable. The filename argument may be a directory name allowing you to check if a directory is writeable.
Keep in mind that PHP may be accessing the file as the user id that the web server runs as (often 'nobody'). Safe mode limitations are not taken into account.
The results of this function are cached. See clearstatcache() for more details.
This function will not work on remote files; the file to be examined must be accessible via the server's filesystem.
See also is_readable().