+ ct_xz, + ct_zstd there should be a comma after ct_zstd. compilers can accept this now.
You are missing concatenation -A support. Zstd has special compatibility with concatenation (read the man page) and as such you should change the tar man page to document that -A works with zstd, and make sure -A works with .tar.zstd archives. -Shawn Landden
