Wine/Proton logging behaviour

What does Proton (and Wine, while we're on the subject) log by default if you set

PROTON_LOG=1

PROTON_LOG=1

but do not set

WINEDEBUG

WINEDEBUG

? I've been able to find information about Wine debug (logging) channels on the official Wine wiki, but nothing about the default behaviour.
- https://gitlab.winehq.org/wine/wine/-/wikis/Wine-User's-Guide#winedebug-channels
- https://gitlab.winehq.org/wine/wine/-/wikis/Debug-Channels