/usr/share/pandoc/data/templates/default.plain is in pandoc-data 1.19.2.4~dfsg-1build4.
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 19 20 21 | $if(titleblock)$
$titleblock$
$endif$
$for(header-includes)$
$header-includes$
$endfor$
$for(include-before)$
$include-before$
$endfor$
$if(toc)$
$toc$
$endif$
$body$
$for(include-after)$
$include-after$
$endfor$
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