[billpg]

Do any formats using ZIP as the underlying format use ZIP comments for metadata? Unless there's a lot of compressors leaving "Zip file generated by MySuperZipper™" then I imagine any comments left were probably done for a good reason.

[ebolyen]

I'm not aware of any, but it wouldn't be insane to build a seekable deflate implementation by defining offsets in a zip comment. This would leave the zip file backwards compatible to usual decompression while allowing internal seeking within an individual file if the decompressor was aware of this index.

[mxmlnkn]

For seekable gzip indexes in zip, there SOZip: https://github.com/sozip/sozip-spec . However, it stores the indexes as files succeeding the actual file entry. To hide these index files and avoid extraction, they are not listed in the central directory, but a linear scan of the local headers, which some wrongly-behaved ZIP tools do, or which might be necessary for recovering broken ZIP files, would find those hidden indexes.