If we would slice this procedure for the statement INC(i) within the WHILE loop, everything that is underlined would be highlighted and be included into the slice of this procedure with respect to the statement INC(i).
We see that the including WHILE loop is part of the slice, the preceding definitions of i and len are part of the slice and the finally the procedure itself with all accessed parameters and local variables is part of the slice.
We clearly see the parts that are relevant to the process of iteration over all numbers of a vector. Everything else is not highlighted.