Be sure to read the documentation if you have not followed the gnuplot development for a long time. Then it has been integrated to the sources available through SourceForge. The mouse support for X11 terminal is available since January 2000. The usage of the mouse is mainly self-explanatory. The mouse is turned on and off with the hotkey 'm'.
Some keys are pre-bound to builtin functions which can be overridden.
This is useful, if several gnuplot versions exist on one system. Setting these will override the command line or Xresource settings. This option is used when plotting permanent labels with Button 2. The readline interfaces were modified to listen to both stdin and the ipc file descriptor. This will not be a major drawback, as 2.2 is out for years now and the current gnu readline version is 4.0.