This method is called by __create_template_vars_index.
        Once the index is created, self.nav_bar_section_page is available for each page.

def __create_lists_for_nav_bar(self):
        """This method is called by __create_template_vars_index.
        Once the index is created, self.nav_bar_section_page is available for each page."""
        
        nav_bar_section = []
        nav_bar_section_page = []
        for key in self.sections:
            nav_bar_section.append(key)
            nav_bar_page = []
            for page in self.sections[key].pages:
                nav_bar_page.append(page)
            nav_bar_section_page.append(nav_bar_page)
        
        nav_bar_section_page_len = [len(x) for x in nav_bar_section_page]
        
        self.nav_bar_section_page = nav_bar_section_page # create a variable for later
        
        # nav_bar_page is a list of lists
        return nav_bar_section, nav_bar_section_page, nav_bar_section_page_len