// the subslices between those separators.
// If sep is empty, SplitN splits after each UTF-8 sequence.
// The count determines the number of subslices to return:
//   - n > 0: at most n subslices; the last subslice will be the unsplit remainder;
//   - n == 0: the result is nil (zero subslices);
//   - n < 0: all subslices.
//
// To split around the first instance of a separator, see [Cut].