Event Triggered?

Hi all

Please tell me in the below code i mentioned which is the first event that gets triggered.I think its AT-SELECTION-SCREEn event.

REPORT ZPRE_5 .

tables:s026.

parameters:wrbtr1 type bseg-wrbtr.

at selection-screen .

if wrbtr1 is initial.

MESSAGE 'Please enter a value' TYPE 'E'.

endif.

START-OF-SELECTION.

Write:/ 'Hi1'.

Write:/ 'Hi2'.

END-OF-SELECTION.

With Regards

Vijay G