This class is then used to build proper css class names used around the UI. For example, entering "protoss" in class's css name will result in category on categories lists and threads in this class on threads list having
list-group-item-category-protoss css classes on them, allowing you to differentiate this category and its threads on lists. In addition to this, such category's page and its thread page would have
page-thread-protoss classes so you could customize it further.