Hit CTRL+D and if all the green brushes disappear they are detail brushes, the remaining black ones will be structural. (CTRL+D to make the come back as well)
Control D will hide all your detail brushes from your view. Making brushes detail is useful because those brushes will not be seen by the vis compiler -- makes it compile faster. However, you do not want to turn everything detail. Major walls should not be detail because they help to block the player's view in the game (higher frame rate). On the other hand, small things like steps should be detail because vis has a hard time compiling the tiny spaces around them.
I understand why steps should be detail brushes, but if removing the steps meant an opening between two rooms would you add a structual brush behind it? Or maybe one of those vis brush thingys?
A hint brush is structural and not solid but if you can use a caulked brush to seal the hole as hint brushes are used only for the vis compile and it is my belief that they are removed (or they may as well be) after compile . They are only used to determine where cuts are made for vis .
