Documentation of the APPX/MSIX format

Last week I unzipped an APPX/MSIX file and zipped them again. The files themselves unchanged. When trying to install the first file, it gave me some signature error, but I think I can solve that one by adding the right files. However, when I clicked the second file (my self-made zip), it gave me some parsing error. When comparing the zip files with each other, I saw some differences.

Is there any documentation about the requirements of the zip file? What files should be stored, what files should be deflated, what files shouldn't have any flags and what files should have flag 0x08? What should be the order of the files? What files need a signature header? Etcetera, etcetera. I think it is really important if you want to make software that also is able to generate APPX/MSIX files.

For now, this what worked for me (in this order):

LocalFileHeader: AppxBlockMap.xml (Deflated, no flags)
LocalFileHeader: AppxManifest.xml (Deflated, flag 0x08)
Signature: crc, compressed_size, uncompressed_size
LocalFileHeader: [Content_Types].xml (Deflated, no flags)

CentralFileHeader: AppxBlockMap.xml (Deflated, no flags)
CentralFileHeader: AppxManifest.xml (Deflated, flag 0x08)
CentralFileHeader: [Content_Types].xml (Deflated, no flags)
EndOfCentralDirectory: ...

I did some tests and for now it seems I have to stick to this order, have the flags as given above, have a correct CRC in both LocalFileHeader and CentralFileHeader and have a version that is the same in both LocalFileHeader and CentralFileHeader, no matter the value.

However, if it is possible to documentate this rules somewhat more, it would be great. Anyway, I will add my findings in this thread for if this rules aren't known by somebody else here.

Start from issue #572 and review its APPX/MSIX examples, including AppxBlockMap.xml, AppxManifest.xml, [Content_Types].xml, LocalFileHeader, CentralFileHeader, Signature, and EndOfCentralDirectory. Compare the reported ZIP differences and document the required files, compression, flags, ordering, headers, CRCs, and versions; done means the format requirements are recorded clearly enough for generators.