Selection Screen using parameter statement

selection-screen begin of block a1 with frame title text-001.
selection-screen begin of line.
selection-screen:
COMMENT 1(20) text-tst FOR FIELD p_date2,
POSITION 33.
parameters: p_date2 LIKE T549Q-begda.
selection-screen POSITION 39.
selection-screen:
COMMENT 52(3) text-and FOR FIELD p_date1,
POSITION 58.
parameters: p_date1 LIKE T549Q-begda.
selection-screen POSITION 64.
selection-screen end of line.
selection-screen end of block a1.