/usr/share/source-highlight/function.lang is in libsource-highlight-common 3.1.7-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | vardef FUNCTION = '([[:alpha:]]|_)[[:word:]]*(?=[[:blank:]]*\()'
function = $FUNCTION
|