`NONE`::
`N`::
    Logging is disabled.

`FATAL`::
`F`::
    Severe errors that lead the execution to abort immediately.
+
This level should be enabled in production.

`ERROR`::
`E`::
    Errors that might still allow the execution to continue.
+
Usually, once one or more errors are reported at this level, the
application, plugin, or library won't perform any more useful task, but
it should still exit cleanly.
+
This level should be enabled in production.

`WARN`::
`WARNING`::
`W`::
    Unexpected situations which still allow the execution to continue.
+
This level should be enabled in production.

`INFO`::
`I`::
    Informational messages that highlight progress or important states
    of the application, plugins, or library.
+
This level can be enabled in production.

`DEBUG`::
`D`::
    Debugging information, with a higher level of details than the
    `TRACE` level.
+
This level should :not: be enabled in production.

`TRACE`::
`T`::
    Low-level debugging context information.
+
This level should :not: be enabled in production.
