zsh-completions

Modern shells, such as bash or zsh, support specifying completion through external files or scripts that the shell can parse. Having never written one, I'm not familiar with the exacts, but suffice it to say the right file in the right location with the right contents can inform the shell as to how to auto complete. i.e., the auto-completion facilities are general / extensible. Especially if many programs follow a general format of program subcommand arg arg arg --optional-flag --option (my personal favorite, as I find it most clear; followed by e.g., argparse in Python, git, many GNU utilities) then it should be easy to see how a small specification of what subcommands take what for args or options should be enough to enable a pretty powerful auto-complete. (This is an example; I think zsh's autocompleters are actually small scripts;