Creates a reference to a run loop source used to convey font requests from the Font Manager.
- macOS 10.6+
- Core Text
The order of the created run loop source.
A block to handle the font request.
A reference to a CFRunLoopSource object that should be added to the run loop. To stop receiving requests, invalidate this run loop source. Returns
NULL on error, in the case of a duplicate
request, or invalid context structure.