Settings: The setting property is reserved for custom setting implementations in themes. The Garland theme provides a theme setting for the type of layout(fixed or fluid), which the site administrator can choose. While we won’t be covering custom theme settings, we highly recommend checking out the
Omega (http://drupal.org/project/omega) and Fusion
(http://drupal.org/project/fusion) themes to get an idea of how theme settings can be used. For more information, visit
http://drupal.org/node/177868.