Created by: simPod
I personally think names should be as much descriptive as possible and that applies for classes as well. I don't fancy naming display class names as .d* so I changed it to .display*.
.d* reminded me my old ways of programming like naming variable containing User object as $u instead of $user or even worse UserModel as $um instead of $userModel The problem with this usually becomes when there's another object with same first letters. eg. UserManager and UserModel. Someone resolves it with $um and $um2 which is not the best way to solve it :)
So IMO class name should say what it does. .display-sm-none says it very well I think. For .d-sm-none I would have to search the docs if I'm user not familiar with Boostrap.