ABAP doubts/questions in developing Cusotmer Exit

Question

Hi,
I found a customer exit for variables in one of the SDN docs and I have few ABAP questions in it. Function exit is EXIT_SAPLRRS0_001 and Include ZXRSU01. I would really appreciate if someone can help me with it.
1.     What exactly is an Include? As in this case ZXRSU01?
2.     What is the difference in the declaration DATA: xyz type d and DATA: xyz like ..
3.     I have two declarations in a user exit DATA: L_S_RANGE TYPE RSSR SRANGESID and LOC_VAR_RANGE LIKE RRRANGEEXIT. What does RSSR SRANGESID and RRRANGEEXIT correspond to?
4.     What is I_STEP, there is a statement which says I_STEP=2. What are the all the possible values for I_STEP. As in 2 here is after the popup.
5.     Also what exactly is I_STEP?
6.     What does I_VNAM and I_T_VAR_RANGE correspond to? (If I am not wrong it corresponds to variable name)
7.     From where can I get a list of all such standard variables like I_STEP, I_VNAM…
Thank you,
sam

Answer 1

Your explanation is good. But right now I am working developing a customer exit for BEx variable. Can you please explain questions above in context to the code below:
DATA: L_S_RANGE TYPE RSR_S_RANGESID.
DATA: LOC_VAR_RANGE LIKE RRRANGEEXIT.
Data: v_loc_date type d.
Data: v_loc_date1 type d.
Data: v_loc(4) type c.
CASE I_VNAM.
to calculate "month to date" user input is "Calday" Key Date
WHEN 'ZPUTMNTH'.
IF I_STEP = 2. "after the popup
LOOP AT I_T_VAR_RANGE INTO LOC_VAR_RANGE
WHERE VNAM = 'ZPDATE'.
CLEAR L_S_RANGE.
L_S_RANGE-LOW = LOC_VAR_RANGE-LOW(6). "low value, e.g.YYYYMM (200606) part of key date (20060625)
L_S_RANGE-LOW+6(2) = '01'. “ low value e..g. YYYYMM01 (20060601)
L_S_RANGE-HIGH = LOC_VAR_RANGE-LOW. "high value = input
L_S_RANGE-SIGN = 'I'.
L_S_RANGE-OPT = 'BT'.
APPEND L_S_RANGE TO E_T_RANGE.
EXIT.
ENDLOOP.
ENDIF.
Thank you,
sam