$language: The language the site is being displayed in.
$site: The name of the site, always filled in.
$head: HTML as generated by drupal_get_html_head() (needed to dynamically add scripts to pages)
$onload_attributes: Onload tags to be added to the head tag, to allow for autoexecution of attached scripts.
$directory: The directory the theme is located in , ie: themes/box_grey or themes/box_grey/box_cleanslate
$logo: The path to the logo image, as defined in theme configuration.
$site_name: The site name of the site, to be used in the header, empty when display has been disabled.
$site_slogan: The slogan of the site, empty when display has been disabled.
$search_box: True(1) if the search box has been enabled.
$search_url: URL the search form is submitted to.
$search_button_text: Translated text on the search button.
$search_description: Translated description for the search button.
$title: Title, different from head_title, as this is just the node title most of the time.
$primary_links (array): An array containing the links as they have been defined in the phptemplate specific configuration block.
$secondary_links (array): An array containing the links as they have been defined in the phptemplate specific configuration block.
$breadcrumb: HTML for displaying the breadcrumbs at the top of the page.
$tabs: HTML for displaying tabs at the top of the page.
$messages: HTML for status and error messages, to be displayed at the top of the page.
$layout: This setting allows you to style different types of layout ('none', 'left', 'right' or 'both') differently, depending on how many sidebars are enabled.
$help: Dynamic help text, mostly for admin pages.
$styles: Required for stylesheet switching to work. This prints out the style tags required.
$mission: The text of the site mission.
$is_front: True if the front page is currently being displayed. Used to toggle the mission.
$sidebar_left: The HTML for the left sidebar.
$content: The HTML content generated by Drupal to be displayed.
$sidebar_right: The HTML for the right sidebar.
$footer_message: The footer message as defined in the admin settings.
$closure: Needs to be displayed at the bottom of the page, for any dynamic javascript that needs to be called once the page has already been displayed.