It may seem a silly question, but unfortunately php4's get_class function returns all lowercase results. When browsing from one page to another, page objects often need to include classes of objects that somehow played a role in the previous page. To do that on a file system that is case sensitive (like Linux's), class names must be in the original case. So the framework needs to know the original class name, the lower case result of the get_class function won't do.
We solved this problem with the includeClass function. This function not only knows how to convert a class name into a file name; it also remembers all names of all classes it includes, in the original case. This way the framework can look up the original class name.