This file is indexed.

/usr/share/doc/cadabra/reserved/regex.tex is in cadabra 1.39-0.2ubuntu2.

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
\cdbreserved{regex}{}

Denotes a regular expression name pattern. The first argument is a
symbol and the second argument is a string containing the regular
expression.