Logger.log
You're seeing just the macro
log, go back to Logger module for more information.
Logs a message with the given level.
Returns :ok.
The macros debug/2, info/2, notice/2, warning/2,
error/2, critical/2, alert/2, and emergency/2 are
preferred over this macro as they can automatically eliminate
the call to Logger altogether at compile time if desired
(see the documentation for the Logger module).