Equivalent to a header guard in C/C++ Used to prevent the class/module from
being loaded more than once
Required files
yaml
stringio
fileutils
little-plugger
logging/appender
logging/layout
logging/log_event
logging/logger
logging/repository
logging/root_logger
logging/stats
logging/color_scheme
logging/appenders
logging/layouts
logging/proxy
logging/config/configurator
logging/config/yaml_configurator
logging/rails_compat