Returns, for a specified URL, the document type identifier to use when opening the document at that location, if successful.
- macOS 10.4+
The URL to use for locating the type identifier.
An error returned if the type identifer could not be determined; otherwise, nil.
The URL is represented by
url. If not successful, the method returns
nil after setting
out to point to an
NSError object that encapsulates the reason why the document type could not be determined, or the fact that the document type is unrecognized.
You can override this method to customize type determination for documents being opened.