public function attributesstring (
        string $tagName, 
        array $attributes = [], 
        array $valid = [], 
        bool $prefixed = true) : self
    {
        foreach ($attributes as $name => $value) {
            if ($this->validate and sizeof($valid) > 0) {
                if (! in_array($name, $valid)) {
                    throw new Exception("Open Graph: Invalid attribute '{$name}' (unknown type)");
                }
            }

            $value = $this->convertDate($value);

            $this->tags[] = $this->createTag($tagName.':'.$name, $value, $prefixed);
        }

        return $this;
    }