Over at #1289536: Switch Watchdog to a PSR-3 logging framework we introduce the concept of "channels" that so far they were the types or the first argument of the watcdog() function.
The big difference, though is that before this, you could use any string as type and it would just work.
With the patch there though, one has to register a service with just a different constructor argument before using that channel.
See comments #208 and #201 above