`TRACE_EMERG`::
    System is unusable.

`TRACE_ALERT`::
    Action must be taken immediately.

`TRACE_CRIT`::
    Critical conditions.

`TRACE_ERR`::
    Error conditions.

`TRACE_WARNING`::
    Warning conditions.

`TRACE_NOTICE`::
    Normal, but significant, condition.

`TRACE_INFO`::
    Informational message.

`TRACE_DEBUG_SYSTEM`::
    Debug information with system-level scope (set of programs).

`TRACE_DEBUG_PROGRAM`::
    Debug information with program-level scope (set of processes).

`TRACE_DEBUG_PROCESS`::
    Debug information with process-level scope (set of modules).

`TRACE_DEBUG_MODULE`::
    Debug information with module (executable/library) scope (set of units).

`TRACE_DEBUG_UNIT`::
    Debug information with compilation unit scope (set of functions).

`TRACE_DEBUG_FUNCTION`::
    Debug information with function-level scope.

`TRACE_DEBUG_LINE`::
    Debug information with line-level scope (default log level).

`TRACE_DEBUG`::
    Debug-level message.