Until proper documentation is created, refer to the Message and Property Reference. The fluent builders are based largely on that documentation, so most concepts should map over.
The prebuild output file contains build-time data that has been dumped for run-time use. This file is auto-generated. Any changes to the file will be lost on the next build.
If you need to modify this file, modify the output-prebuild-vars command. To test your changes, delete the prebuild output file, then run yarn test-check or yarn compile.