You'll probably need to ask a Wordpress group or forum. Wordpress uses PHP, but it's a highly customized application. Unless someone here has a good grasp on the inner workings of Wordpress, you won't find anyone willing to take your question.
For example, the following are custom functions, not PHP functions: is_home(), bloginfo(), wp_list_categories(), in_category(), wp_list_pages() ... unless I'm totally out of the loop (haven't been around programming much lately), that's every function in the PHP code.