Tabs on selection screen

Report ZTEST.

DATA flag(1) TYPE c.
* SUBSCREEN 1
SELECTION-SCREEN BEGIN OF SCREEN 100 AS SUBSCREEN.
SELECTION-SCREEN BEGIN OF BLOCK b1 WITH FRAME.
PARAMETERS: Field1(20) TYPE c,
Field2(20) TYPE c,
Field3(20) TYPE c.
SELECTION-SCREEN END OF BLOCK b1.
SELECTION-SCREEN END OF SCREEN 100.

* SUBSCREEN 2
SELECTION-SCREEN BEGIN OF SCREEN 200 AS SUBSCREEN.
SELECTION-SCREEN BEGIN OF BLOCK b2 WITH FRAME.
PARAMETERS: q1(20) TYPE c ,
q2(20) TYPE c ,
q3(20) TYPE c .
SELECTION-SCREEN END OF BLOCK b2.
SELECTION-SCREEN END OF SCREEN 200.

* STANDARD SELECTION SCREEN
SELECTION-SCREEN: BEGIN OF TABBED BLOCK mytab FOR 10 LINES,
TAB (20) button1 USER-COMMAND push1,
TAB (20) button2 USER-COMMAND push2,
END OF BLOCK mytab.

INITIALIZATION.

button1 = 'TAB1'.
button2 = 'TAB2'.
mytab-prog = sy-repid.
mytab-dynnr = 100.
mytab-activetab = 'BUTTON1'.

AT SELECTION-SCREEN.

CASE sy-dynnr.
WHEN 1000.
CASE sy-ucomm.
WHEN 'PUSH1'.
mytab-dynnr = 100.
mytab-activetab = 'BUTTON1'.
WHEN 'PUSH2'.
mytab-dynnr = 200.
mytab-activetab = 'BUTTON2'.
ENDCASE.
WHEN 100.
MESSAGE s888(sabapdocu) WITH text-040 sy-dynnr.
WHEN 200.
MESSAGE s888(sabapdocu) WITH text-050 sy-dynnr.
ENDCASE.

MODULE init_0100 OUTPUT.

LOOP AT SCREEN.
IF screen-group1 = 'MOD'.
CASE flag.
WHEN 'X'.
screen-input = '1'.
WHEN ' '.
screen-input = '0'.
ENDCASE.
MODIFY SCREEN.
ENDIF.
ENDLOOP.
ENDMODULE.
MODULE user_command_0100 INPUT.
MESSAGE s888(sabapdocu) WITH text-050 sy-dynnr.
CASE sy-ucomm.
WHEN 'TOGGLE'.
IF flag = ' '.
flag = 'X'.
ELSEIF flag = 'X'.
flag = ' '.
ENDIF.
ENDCASE.
ENDMODULE.

START-OF-SELECTION.

WRITE: / 'Field1:', Field1,'Q1:', q1,
/ 'Field2:', Field2,'Q2:', q2,
/ 'Field3:', Field3,'Q3:', q3.