Side note on this function: if you extend.split a line not containing any of the S.Separators you will still get the line in the resulting table. This is not the same as an extend.range for instance.
Script to illustrate this case: https://try.lokad.com/s/extend.split

Sorry my link was private, please find here the shareable one: https://try.lokad.com/s/extend_split_example

That is not true if you split at the read stage. In that case, the line is dropped if you have nothing to split on.

If you have nothing to split on (the cell is empty) then the line is dropped. If you have a content but no occurence of the separator, the line is kept (= splitted over 1 line).