// the positions of the first and last items of the radio group this item
// belongs to or -1: start is the radio group start and is valid for all
// but first radio group items (m_isRadioGroupStart == FALSE), end is valid
// the positions of the first and last items of the radio group this item
// belongs to or -1: start is the radio group start and is valid for all
// but first radio group items (m_isRadioGroupStart == FALSE), end is valid