Filter events going to the logging buffer. This is a packed
bit string object of which each bit has the following meaning:
(bit 0 is the least significant bit).
bit position meaning
------------ -------
8-31 reserved
7 Warning (warning conditions)
6 Notification (normal but significant conditions)
5 Informational (informational messages)
4 Error (error conditions)
3 Emergency (system is unusable)
2 Debugging (debugging messages)
1 Critical (critical conditions)
0 Alert (immediate action needed)
Setting a critical level bit to 1 makes the logging buffer
accept the corresponding event. Resetting a critical level
bit to 0 makes the logging buffer reject the corresponding
event.