Manual:$wgSpecialPages

Details
$wgSpecialPages stores a list of custom special pages defined for a MediaWiki installation. The array is keyed by a non-localized id for the special page. The values assigned to each key may take one of the following forms:


 * string: a string containing the name of a subclass of SpecialPage.
 * array: an array where the first element is the name of the subclass and all remaining elements are parameters that should be passed to the constructor of that subclass.
 * callback: (since MW 1.24, ) expected to return a  instance. Useful for full control over the special page's construction parameters.

For more information, please see SpecialPage.php