///
bool idxUpDown(Cursor &, bool up) const;
///
bool idxBackward(Cursor &) const { return false; }
///
bool idxForward(Cursor &) const { return false; }
///
bool idxUpDown(Cursor &, bool up) const;
///
bool idxBackward(Cursor &) const { return false; }
///
bool idxForward(Cursor &) const { return false; }