code: func (s *SortFilter) Text(n int) *SortFilter {
  	s.add(func(a, b string) int {
  		a1, a2 := column(a, n)
  		b1, b2 := column(b, n)
  		switch {
  		case a1 < b1:
  			return -1
  		case a1 > b1:
  			return +1
  		case a2 < b2:
  			return -1
  		case a2 > b2:
  			return +1
  		}
  		return 0
  	})
  	return s
  }
docs: // Text sets the next sort key to sort by column n in lexicographic
  // order. Column 0 means the entire string. Items that do not have
  // column n sort to the front.