The operating system source tree includes hundreds of repositories. Many of these - are only used for debugging, testing or development and are not actually part of what - gets used for building a production release. The manifest repository references all of - these. Most of these are used unmodified from the Android Open Source Project (AOSP). - A few dozen of the repositories including most of the core OS are either forked from - AOSP or are unique to GrapheneOS.
+The operating system source tree includes hundreds of repositories. Many of + these are only used for debugging, testing or development and are not actually + part of what gets used for building a production release. The manifest repository + references all of these. Most of these are used unmodified from the Android Open + Source Project (AOSP). A few dozen of the repositories including most of the core + OS are either forked from AOSP or are unique to GrapheneOS.
The operating system has a unified build system, but some components like Chromium are too complex to fit into it so they're included as prebuilts instead