Manual:MWNamespace.php

Namespace.php contains the MWNamespace class, a utility class with only static functions for dealing with man-ns>Special:MyLanguage/Manual:Namespace|namespaces that encodes all the "magic" behaviors of them based on index.

Methods
Returns an array of the namespaces (by integer id) that exist on the wiki. Used primarily by the api in help documentation. This function calls  without using the rebuild option and it then excludes the negative number namespaces, e.g. -1 (special page).
 * : Returns array of all defined namespaces with their canonical (English) names.
 * : Returns the canonical (English) name for a given index