Returns the location of the localized reference documentation that describes the filter.
- iOS 9.0+
- macOS 10.4+
- UIKit for Mac 13.0+Beta
- tvOS 9.0+
- Core Image
The filter name.
A URL that specifies the location of the localized documentation, or
nil if the filter does not provide localized reference documentation.
The URL can be a local file or a remote document on a web server. Because filters created prior to OS X v10.5 could return
nil, you should be make sure that your code handles this case gracefully.