Going back to marking it semi solved. If, and only if, I create the file as root, it works. If I create the file as user1 and then, even have root set the acl, user100 cannot write to it. But, if I create the file as root, and then, set the acl as root, it works and user100 can open it in vi, write to it and save it. So, I’ll mark this as a solution in case anyone does a webserch for it.