Sorry, the wording on the repo could probably be revised. The zip header is a required part of the archive, and without it the rest of the data could be lost f

Sorry, the wording on the repo could probably be revised. The zip header is a required part of the archive, and without it the rest of the data could be lost forever. .xpr archives have no header and (currently) no offsets. The compression settings can be inferred from the data inside the archive itself, making headers that describe the data unnecessary. And while it's true that you can decompress old archives with new hardware, you can't always decompress a new archive on outdated software. Sometimes even with up-to-date software it's possible to sometimes create an archive with 7z on Linux that WinRar on Windows will not be able to open.