When creating the subwindow, begin_y and begin_x are relative to the entire terminal screen. If either numlines or numcols is 0, then the subwin function sets that dimension to (LINES - begin_y) or (COLS - begin_x), respectively. The window pointed to by win must be large enough to contain the entire area of the subwindow. Any changes made to either window within the coordinates of the subwindow appear on both windows.