/usr/share/vim/addons/doc/dockerfile.txt is in vim-syntax-docker 17.12.1-0ubuntu1.
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 6 7 8 9 10 11 12 13 14 15 16 17 18  | *dockerfile.txt*  Syntax highlighting for Dockerfiles
Author: Honza Pokorny <https://honza.ca>
License: BSD
INSTALLATION                                                     *installation*
Drop it on your Pathogen path and you're all set.
FEATURES                                                             *features*
The syntax highlighting includes:
* The directives (e.g. FROM)
* Strings
* Comments
 vim:tw=78:et:ft=help:norl:
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