Wow, finally a universal display link across macOS an iOS. That's a big deal if you've ever had to translate between CVDisplayLink and CADisplayLink. CV doesn't have any frame rate controls, and this one has that and latency controls.

This is also a problem. os/log.h needs a warning level just like the compiler and all standard logging systems. No matter how much os_log wants to argue to not have one. Having to translate to default, error, fault is not good. Logger.warning() This method is functionally equivalent to the error(_:) method.