public function append(string $str, string $mime = "text/html")
    {
        // To append, we need to make sure we have a string first
        if (empty($this->output[$mime]) || !is_string($this->output[$mime]))
            $this->output[$mime] = $this->getOutput($mime);

        $this->output[$mime] .= $str;
        return $this;
    }