public void ReplaceWithRange(T from, T to)
{
var iFrom = _allItems.IndexOf(from);
var iTo = _allItems.IndexOf(to);
if (iFrom < 0 || iTo < 0)
{
return; //normally unreachable code
}
if (iFrom > iTo)
{
var tmp = iFrom;
iFrom = iTo;
iTo = tmp;
}
_selectedItems.Replace(
_allItems.Skip(iFrom).Take(iTo - iFrom + 1));
}