The option groups are used for creating the mutually exclusive group of items for selection. It is very similar functionality to the Option Buttons on Windows Forms. The group is defined as a set of items with the same parent that have OptionGroup property set to the same string value. The option group functionality will then set the Checked property automatically on this set of item so only one item is checked at a time.
The Checked property is set based on user clicking the item. The item that was clicked will have its Checked property set to true, and the item that is in the same group that was previously checked will have its Checked property set to false.