/usr/share/source-highlight/bib.lang is in libsource-highlight-common 3.1.8-1.2.
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 | state bibtex = '@[[:alpha:]]+(?=\{)' begin
argument = '(?<=\{)[[:alnum:]-]+'
normal = "," exit
end
string = '[[:alpha:]]+(?=[[:blank:]]*=)'
|