The sub-window shows different information depending on the running mode of the application: * if the application is running in debug mode, it shows the stack trace of the exception. * if the application is running in production mode, it shows a code to report that can be found in log files. The dialog (ErrorWindow) can be automatically invoked through an error handler configured by `com.flowingcode.vaadin.addons.errorwindow.VaadinServiceInitListenerImpl` or just by itself calling `ErrorManager.showError()`. It is also possible to use the ErrorWindow directly for messages customization purposes.