Radio button form fields belong to the generic classes of form field called "Toggle Buttons" if owned by an object other than an option box form field, or "Option Buttons" if owned by an option box form field. They are most commonly used for supporting On/Off or True/False type data values, although they are not restricted to these value types. Multiple radio buttons owned by the same parent object cannot be in the "On" state simultaneously.
Radio buttons can be text-based or image-based. Text radio buttons are displayed as the familiar "circle" immediately followed by some descriptive text. The value state of a text radio button is "On" if the circle portion contains another solid circle and "Off" if no solid circle is present. Image radio buttons are displayed as an image with no associated text or circle portion. The value state of an image radio button (more appropriately, "image toggle button" or "image option button") is determined by which one of the two possible images is displayed. The physical dimensions of an image radio button are controlled by the selected automatic sizing option.