How to know whether a line in a list is header / footer / data line?

Dear All,

I have a list with header and footer lines. The lines that contains the actual data has a check box column. Due to the page size I'm using, all of my data will be shown in several pages with each page has header and footer lines.

What I'm doing is to read the check box in each line by using the following code:

  DO.
    ...
    READ LINE sy-index LINE VALUE INTO wa.
    ...
    IF wa-mark IS NOT INITIAL.
    ...

The field 'mark' is the check box field.

The problem here is the header and footer lines are also read by the READ LINE sy-index LINE VALUE INTO wa statement while I want to treat header and footer lines specially.

Is there any way to mark a line as header / footer / data line?

Thanks in advance,

Haris