I'm 'upgrading' my web application towards a Progressive Web Application by including a Web App Manifest. I'm particularly interested in the start_url argument since my application behaves slightly differently if the bookmarked URL includes a user-determined parameter specifying a location. Think https://www.example.com?location=Amsterdam. In short, I can't include the user's interest in the generic start_url argument in a static Web App Manifest, since it differs per user: https://www.example.com?location=Amsterdam, https://www.example.com?location=London, https://www.example.com?location=Paris.
The documentation on start_url is a bit confusing, as web.dev from Google Developers mentions: "The start_url is required and tells the browser where your application should start when it is launched, ..." The oft-done suggestion is that start_url equals "/" to the root of the web application.
MDN from Mozilla mentions start_url as not mandatory, and includes a note "The start_url member is purely advisory, and a user agent may ignore it or allow the user to alter it at install time or afterwards."
So, which is it? Is start_url required / mandatory, or not?