chktex: how to add an output format with newline

Question

I am using chktex to check my latex files. Now I want to define my own output format instead of choosing from given ones with -v<number>. This is via the option -f. The problem is, that I cannot specify a newline. For example

chktex -f%k%b%f(%l.%c)%n%b%m xxx.tex

writes all warnings or what so ever in a single line. The format specifier resembles a bit C and %b is boundary. The rest, %k%f(%l.%c)%n%m writes the Kind of message, the Filename, Line and column in (...) followed by message Number and Message.

What is missing is a newline to put output for each message on a separate line. I tried \n and variants first, but does not work. I saw in chktexrc the specifications are given in a form !n signifying newline.

Unfortunately, my C programming skills are not sufficient to answer my question myself from the source in https://git.savannah.gnu.org/git/chktex.git, but maybe someone is motivated to find out.