Bash completion for the domterm command (a terminal emulator) calls the domterm command itself with a special "#complete-for-bash" option:

    complete -o nospace -C 'domterm "#complete-for-bash" "$COMP_LINE" "$COMP_POINT"' domterm

It works pretty well has the advantage that it automatically ties the completion to the executable, avoiding version mismatches.

It would be great if other shells could use a similar mechanism. Then you could use the same completion logic for multiple shells. A complication is that zsh and fish completion provide descriptive help text; there would need to be a mechanism for a "completion option" to provide such help text.