Every Wiki Group can have a Group Header page that contains markup that should be included at the beginning of each page within the group. This feature is primarily used for:
adding a disclaimer or heading to all of the pages of a group
defining custom Wiki Styles that may be used for all pages in a group
replacing the default headers and/or footers for pages in a group (using [[noheader]] and [[nofooter]] -- see Special Markups)