To report errors, the Logger class is available which works mostly like an iostream. Example usage is as shown above in the RandomBackend. Note that it is very important that each line is ended with endl as your message won't be visible otherwise.

To indicate the importance of an error, the standard syslog errorlevels are available. They can be set by outputting Logger::Critical, Logger::Error, Logger::Warning, Logger::Notice, Logger::Info or Logger::Debug to L, in descending order of graveness.