A radio button displays a selection indicator (default shape is diamond) to the left if its label. Radio buttons are arranged in groups and are used to select one from a group of mutualy exclusive choices, such as one of the several fonts or one of several colors. Associate to each group of radio buttons there is one internal group variable.
When Button1 is pressed over a radio button, the group variable is set to the value associated with the radio button and the selection indicator lights up, and its callbacks are invoked.