Android used to have a permission for internet access and when I was building an app that I wanted to prove to people that was local-only, fully offline, it hel

Android used to have a permission for internet access and when I was building an app that I wanted to prove to people that was local-only, fully offline, it helped to show that the app didn't even have permission to access the internet. I wish browsers, Android, and iOS had this option so that users could be confident that the app/site doesn't have access to the internet. Maybe a little tricky with a browser but perhaps it could be possible somehow.