What is the difference between Android's 'install-time' and 'runtime' permissions, and why did Android 6.0 introduce the runtime model?

• A.Install-time permissions apply to system APIs; runtime permissions apply only to third-party APIs and SDKs bundled in the APK
• B.Install-time permissions are granted by the Google Play Store server before download; runtime permissions are granted by the local device OS when the app is first launched
• C.Install-time permissions are permanent and irrevocable; runtime permissions can be revoked by the user but also expire after 30 days and require re-grant
• D.Install-time permissions (normal level) are granted at APK installation without user interaction; runtime permissions (dangerous level, API 23+) are requested in-context when the feature is first used, allowing users to grant/deny individual permissions - introduced to address the 'all or nothing' install model where users had to grant all permissions or not install the app at all