public function registerNamespace(PHPTAL_Namespace $ns)
    {
        $this->namespaces_by_uri[$ns->getNamespaceURI()] = $ns;
        $this->prefix_to_uri[$ns->getPrefix()] = $ns->getNamespaceURI();
        $prefix = strtolower($ns->getPrefix());
        foreach ($ns->getAttributes() as $name => $attribute) {
            $key = $prefix.':'.strtolower($name);
            $this->_dictionary[$key] = $attribute;
        }
    }