CGI is a large class, providing several categories of methods, many of which are
mixed in from other modules. Some of the documentation is in this class, some in
the modules CGI::QueryExtension and CGI::HtmlExtension. See CGI::Cookie for
specific information on handling cookies, and cgi/session.rb (CGI::Session) for
information on sessions.

For queries, CGI provides methods to get at environmental variables, parameters,
cookies, and multipart request data. For responses, CGI provides methods for
writing output and generating HTML.