* Default theme implementation to display a single Drupal page.
* Available variables:
* General utility variables:
* - $base_path: The base URL path of the Drupal installation. At the very
* least, this will always default to /.
* - $directory: The directory the template is located in, e.g. modules/system
* or themes/bartik.
* - $is_front: TRUE if the current page is the front page.
* - $logged_in: TRUE if the user is registered and signed in.
* - $is_admin: TRUE if the user has permission to access administration pages.
* Site identity:
* - $front_page: The URL of the front page. Use this instead of $base_path,
* when linking to the front page. This includes the language domain or
* - $logo: The path to the logo image, as defined in theme configuration.
* - $site_name: The name of the site, empty when display has been disabled
* in theme settings.
* - $site_slogan: The slogan of the site, empty when display has been disabled
* in theme settings.
* - $main_menu (array): An array containing the Main menu links for the
* site, if they have been configured.
* - $secondary_menu (array): An array containing the Secondary menu links for
* the site, if they have been configured.
* - $breadcrumb: The breadcrumb trail for the current page.
* Page content (in order of occurrence in the default page.tpl.php):
* - $title_prefix (array): An array containing additional output populated by
* modules, intended to be displayed in front of the main title tag that
* appears in the template.
* - $title: The page title, for use in the actual HTML content.
* - $title_suffix (array): An array containing additional output populated by
* modules, intended to be displayed after the main title tag that appears in
* the template.
* - $messages: HTML for status and error messages. Should be displayed
* - $tabs (array): Tabs linking to any sub-pages beneath the current page
* (e.g., the view and edit tabs when displaying a node).
* - $action_links (array): Actions local to the page, such as 'Add menu' on the
* menu administration interface.
* - $feed_icons: A string of all feed icons for the current page.
* - $node: The node object, if there is an automatically-loaded node
* associated with the page, and the node ID is the second argument
* in the page's path (e.g. node/12345 and node/12345/revisions, but not
* - $page['help']: Dynamic help text, mostly for admin pages.
* - $page['highlighted']: Items for the highlighted content region.
* - $page['content']: The main content of the current page.
* - $page['sidebar_first']: Items for the first sidebar.
* - $page['sidebar_second']: Items for the second sidebar.
* - $page['header']: Items for the header region.
* - $page['footer']: Items for the footer region.
* @see template_preprocess()
* @see template_preprocess_page()
* @see template_process()