Maybe a bit of a noob question, but I can't find it anywhere (I googled it, and I've tried the handbook, but I might have missed it):
When I install a port and the port asks for configuration options, I can make a selection of the different options. The standard options are selected. However, in front of some of the standard and of the other options there's a red plus sign. What is the meaning of the plus sign in the configuration screen?