/usr/share/zsh/functions/Zle/narrow-to-region-invisible is in zsh-common 5.1.1-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # As narrow-to-region, but replaces the text outside the editable region
# with `...' if it was non-empty. Can be used directly as a widget.
autoload -Uz narrow-to-region
narrow-to-region -p '...' -P '...' -n
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