(PHP 4 >= 4.0.2, PHP 5)
fdf_set_flags — Sets a flag of a field
$fdf_document
   , string $fieldname
   , int $whichFlags
   , int $newFlags
   )Sets certain flags of the given field.
fdf_document
     The FDF document handle, returned by fdf_create(), fdf_open() or fdf_open_string().
fieldname
     Name of the FDF field, as a string.
whichFlags
     
newFlags
     
   成功时返回 TRUE, 或者在失败时返回 FALSE.