WordPress at a glance
action is not described

atom_ns action-hook . WP 2.0.0

Fires at end of the Atom feed root to add namespaces.

Usage

add_action( 'atom_ns', 'action_function_name_4373' );
function action_function_name_4373(){
	// action...
}

Where the hook is called

In file: /wp-includes/feed-atom.php
atom_ns
wp-includes/feed-atom.php 27
do_action( 'atom_ns' );
wp-includes/feed-atom-comments.php 20
do_action( 'atom_ns' );

Where the hook is used (in WP core)

Does not used.