To be honest, there's nothing ground breaking about this project.
The -transformed part of the name comes from the idea of basing the library around
stream.Transform.
It's a bit of a play on the practice of naming a library -as-promised when the library's API is based on Promises.
The idea is that instead using a reader to read from a MARC file or using a writer to write to a MARC file, you instead transform a file into a stream of MARC records or you transform a stream of MARC records into a file.
The flexibility of this approach is that you can source/read from or sink/write to any stream, not just files. And you can freely add any other transforms before or after the MARC transforms.