code: func (p *WebPage) RenderBase64(format string) (string, error) {
  	var resp struct {
  		ReturnValue string `json:"returnValue"`
  	}
  	if err := p.ref.process.doJSON("POST", "/webpage/RenderBase64", map[string]interface{}{"ref": p.ref.id, "format": format}, &resp); err != nil {
  		return "", err
  	}
  	return resp.ReturnValue, nil
  }
docs: // RenderBase64 renders the web page to a base64 encoded string.