code: public function attach($key, $content, $filename)
      {
          $this->request[] = new SimpleAttachment($key, $content, $filename);
      }
docs: Adds a MIME part to the query. Does nothing for a form encoded packet.
  
  @param string $key          Key to add value to.
  @param string $content      Raw data.
  @param hash $filename       Original filename.