title: Can't get right autofill on specific case number
body: <p>I have a column with specific case numbers, which look like 1/2017, 2/2017, etc. The series can go until infinite (I don't know for sure how many cases I will have), but it would be nice to be able to use autofill. If I select the first 3 values and drag down the fill handle, I get 1/2018, 2/2018, 3/2018. I would need exactly the opposite, to linearly change the first number and leave 2017 alone. The formatting of the column is General. Should I create a custom formatting and/or block the changing of the 2017 somehow? (I know that you can block a value of a cell from changing with the <em>$</em> operator)</p>
  
  <p>Thanks.</p>