title: Make an excel cell mandatory, based on value of other 2 cells
body: <p>So.. I've an excel where 2 consecutive cells can be marked with the same value (mostly Text), based on this 2 cells the value of the 3rd cell should be filled mandatorily by the user.</p>
  
  <p>The range of cells can be different as I need to use the same snippet cross many excels.</p>
  
  <p>Any help would be sincerely appreciated.</p>
  
  <p>Many thanks! :)</p>