Actions and Buttons in ``Window'' mode

The ``Main input window'' is created when command GUI$\backslash$GO is typed. Four buttons are defined by default:

• the OK button,
  which sets all variables defined in the main and optional windows. This button also executes the command passed as argument to the GUI$\backslash$GO command (if specified).
• the UPDATE button,
  which sets all variables defined in the main and optional windows, without executing the (optional) command passed as argument to the GUI$\backslash$GO command.
• the ABORT button.
  Variables are not modified, and an error is sent to the main program.
  
• the HELP button.
  This button displays the help file specified in the GUI$\backslash$PANEL command.

Additional buttons can also be added to the ``main window'' using the GUI$\backslash$BUTTON command. Two types of buttons exist

• Buttons with no associated parameters. These buttons appear just after the 3 main buttons.
• Buttons with optional parameters. These buttons appear sequentially with the variables, and have an associated parameter or `` optional'' window. When such a button is defined, all subsequent LET commands create widget in a ``optional'' window. This window is by default hidden, but can be unveiled by the user.

The ``optional'' window provide a way to hide some non-essential parameters, and/or to create a ``main window'' with a control panel defining many actions, each action having its own input window and separate help.