Message is sent to table window to continue selection started by WM_USER_STS. HIWORD(wParam) contains column with current end of selection, LOWORD(wParam) - X offset within the column in character widths, lParam - Y offset within the window in character heigths.
Standard table window should simply pass this message to Tablefunction.
Custom table window must modify data to reflect change of selection but must neither redraw nor invalidate the window. It returns 1 if screen appearance is changed and 0 if not.