In my case, I want to get into a view helper all messages from different namespaces (error, warning, notice, ok). A method like this is very helpful to handle this situation.

/**
 * getCurrentNamespaces() - get all used namespaces
 *
 * @return array
 */
public function getCurrentNamespaces()
{
    return array_keys(self::$_messages);
}
    
/**
 * getNamespaces() - get all used namespaces
 *
 * @return array
 */
public function getNamespaces()
{
    $namespaces = array();
    foreach (self::$_session as $key => $namespace) {
        $namespaces[] = $key;
    }
    return $namespaces;
}