In our project we have a style set for hyperlinks:

defaultSettings.StyleFormats(
                new
                {
                    title = "Action links",
                    items = new[]
                    {
                        new { title = "Internal", selector = "a", classes = "internal" },
                        new { title = "External", selector = "a", classes = "external" },
                        new { title = "Download", selector = "a", classes = "download" }
                    }
                });

The problem we are facing is that you are able to select all three styles at once. How to modify tinyMCE so that you are only able to select one style at a time? 

If you click on Internal, there is a checkmark beside it, when you click on External the checkmark should be beside External instead of Internal. That is our desirable functionality