Specifies the name of the first-level navigation item to which an item corresponding to the required business class is added.
A string value which represents the name of the group within the navigation control.
If the group specified by this property does not currently exist, it is created, and an item is added to it.
If this property is not specified, the default first-level navigation item name is used. This name is specified by the NavigationItemAttribute.DefaultGroupName property.