private function elementBodyClasses(string $element) : string
    {
        if (in_array($element, $this->body_elements) === true) {
            $class = '';

            if (count($this->body_classes[$element]) > 0) {
                if (array_key_exists($element, $this->body_classes_first) === false) {
                    $class = ' ' . implode(' ', $this->body_classes[$element]);
                } else {
                    $class = '';
                    foreach ($this->body_classes[$element] as $body_class) {
                        if (array_key_exists($body_class, $this->body_classes_first[$element]) === false) {
                            $class .= ' ' . $body_class;
                        } else {
                            if ($this->body_classes_first[$element][$body_class] === true) {
                                $class .= ' ' . $body_class;
                                $this->body_classes_first[$element][$body_class] = false;
                            }
                        }
                    }
                }
            }

            return $class;
        } else {
            return '';
        }
    }