private function validElements( $node )
	{
		// The node must be an array
		if ( ! isset( $node ) ) return false;

		// The node may represent a tuple
		if ( XBRL::isTuple( $node['taxonomy_element'] ) ) return true;

		// There must be an element called 'elements'
		if ( ! isset( $node['elements'] ) ) return false;
		// The elements must have some members
		if ( count( $node['elements'] ) === 0 ) return false;

		foreach ( $node['elements'] as $elementKey => $element )
			if ( ! empty( $element['value'] ) /* || is_numeric( $element['value'] ) */ ) return true;
		return false;
	}