Dear Lasse, First of all, thank you for implementing lzip decompression in the xz tool.
I think that you could, if so you wish, simplify the reference to the lzip format in the man page of xz.
For example, the "sync flush marker extension" has never been part of the lzip format specification, and has never been produced by any lzip compressor because it does not make sense in compressed files. I added undocumented support for it to lzip just as a way to test lzlib interactive data streams, and I have removed the support in lzip 1.25. "sync flush" is a lzlib-only feature that does not belong in a lzip (de)compressor.
Similarly, lzip format version 0 was incomplete and inadequate for parallel decompression. As you note in the man page, decompression support for version 0 was removed years ago, and I should have removed it even earlier. I consider all versions of lzip prior to 1.4 obsolete and unsupported. If anybody has the need to decompress a version 0 file, which I very much doubt, he/she may use lzip 1.17 to decompress it, or may ask me for help. I'll gladly convert a version 0 file to version 1 with my text editor.
Therefore, if you wish to simplify the xz man page, I think there is no need to mention the sync flush marker nor the format version 0 of lzip.
Best regards, Antonio.
