PositionAt
int32 position = PositionAt(kNoFocus, where, &newFocus);
int32 start = PositionAt(kNoFocus, where, &newFocus);
int32 end = PositionAt(fFocus, where);
int32 position = PositionAt(fFocus, frame.LeftTop());
int32 position = PositionAt(fFocus, frame.LeftTop());
int32 PositionAt(view_focus focus, BPoint point,