Documentation

Non fatal condition that may indicate a problem.

Display on stderr at normal verbosity and above.

Useful status message.

Display at normal verbosity and above.

This is for the ordinary helpful status messages that users see. Just enough information to know that things are working but not floods of detail.

More detail on the operation of some action.

Display at verbose verbosity and above.

Detailed internal debugging information

Display for deafening verbosity.