The function fsidebar() can be used to load additional data referring to a template.

Using this functxcbvbion loading sidebar data is the most common way, but you also can load a footer, or such, that way. :-)

sidebar(); - E.g. the current page uses a template like subpage.php instead of main.php, the function looks first for subpage.sidebar.php, if this file not exists it looks for sidebar.php and if this file not exists nothing will happen.