The progressbar widget is intended to show the progress of some process. The end goal is the max option specified when creating the widget, which defaults to 100. If we know the size of the data we are processing ahead of time, we would use the max option to reflect this end goal. However, we are sometimes faced with the scenario where we have some processing to do on the client; or, we are waiting for some backend process to complete and send a response back to the client. For example, the user has initiated a backend task using the API, and they're now waiting for a response. The bottom line is, we want to illustrate to the user that progress is being made, and we just don't know how much progress has been made.
To display the fact that progress is being made, despite not knowing how much progress, we need an indicator widget. We can write our own widget to achieve this, extending the progressbar widget, since we can reuse many components there.