I would call this 'SyslogFacility', or, better, move it into the 'SyslogLogger' class. It will be confusing for someone looking at the documentation to see these types at the global scope, left wondering for what they are used.

In fact, I would move all definitions from here up to the `SyslogLogger` class into the class so that it is nicely self-contained, possibly making them all except `Facility` private as it is always easier to add public symbols that it is to remove them (WRT backwards compatibility).