zsh/Completion/Core/_menu

#autoload

[[ _matcher_num -gt 1 ]] && return 1

# This completer is an example showing how menucompletion can be
# implemented with the new completion system.
# Use this one before the normal _complete completer, as in:
#
#   zstyle ":completion:::::" completer _menu _complete

if [[ -n "$compstate[old_list]" ]]; then

  # We have an old list, keep it and insert the next match.

  compstate[old_list]=keep
  compstate[insert]=$((compstate[old_insert]+1))
else
  # No old list, make completion insert the first match.

  compstate[insert]=1
fi

return 1