DEFAULT is the end sentinel.

ERROR is used for situations that require special handling, where normal operation could not proceed as expected.

FATAL is used for situations that require an immedate, hard server shutdown.

INFO is used for informational messages that do not require action.

NONE can be used in filters to specify that no messages should be emitted.

UNKNOWN is populated into decoded log entries when the severity could not be determined.

WARNING is used for situations which may require special handling, where normal operation is expected to resume automatically.