Instead, classes are connected in meaningful ways. It is this connection that makes it possible to follow a chain of information by double-clicking. We noted earlier that every class name in the main window and almost every class member name in the Selection List has this property. In these cases a hint is provided to help you tell the difference between linked and unlinked items. The linked items appear in boldface.
Unlinked items are plain.
Some serve as labels or give structure to the text window. The following pages follow this thread of information a little further.