WordPress at a glance
filter is not described

login_messages filter-hook . WP 2.5.0

Filters instructional messages displayed above the login form.

Usage

add_filter( 'login_messages', 'filter_function_name_218' );
function filter_function_name_218( $messages ){
	// filter...

	return $messages;
}
$messages(string)
Login messages.

Where the hook is called

login_header()
wp-login.php 237
echo '<p class="message">' . apply_filters( 'login_messages', $messages ) . "</p>\n";

Where the hook is used (in WP core)

Does not used.