Describes a radiogroup. A radiogroup may contain radioitems that belong together.
A radiogroup is mapped to a panel with the id of the radiogroup. This panel contains JRadioButtons,
grouped into a ButtonGroup named with the id of the radiogroup concatenated with _buttongroup.
An onchange event occurs when the another radioitem of the radiogroup is selected. When the onchange attribute has the value true, an entry, for handling the onchange event, will be created in the code-frame of the window the popupmenu is in. Allowed values are true and false. The default value is false. The event code is inserted into a shared ActionListener which listens to all the radiobuttons.
Specifies the title to display at the top of the radiogroup.