/usr/share/mercurial/templates/rss/bookmarks.tmpl is in mercurial-common 2.8.2-1ubuntu1.
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 | {header}
<title>{repo|escape}: bookmarks </title>
<description>{repo|escape} bookmark history</description>
{entries%bookmarkentry}
</channel>
</rss>
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