title: How can I add extra column classes in Bootstrap 3?
body: <p>Bootstrap 3 changed the previous approach of <code>span</code> classes for the grid system for the more explicit <code>col-xs</code>, <code>col-md</code>, etc. An excellent improvement imo, but still I find that I would like to add extra column classes. In specific, I want to create a column class for something between <code>col-md</code> and <code>col-lg</code>.</p>
  
  <p>I know that I can change the LESS variables in order to change the lengths of the standard column classes, but I do not want to modify them. Instead I want (if possible) to add extra classes for different screen sizes.</p>
  
  <p>Any suggestions on how to do that? I did some research, but since Bootstrap 3 is quite new, I didn't find anything of that sort.</p>