It would be useful to have the possibility to negate a pattern in the
boring file, so a file that is matched by a regexp in the boring file to
be re-included by the negated pattern.
This is the equivalent of lines starting with `!' in gitignore files.
The idea is that a file should be ignored if it matches a regexp in the
boring file and it does not match a negated regexp (a regexp starting
with `!') in the same file.