Buildservice _constraints

What does the specifying jobs [1] in the _constraints file actually do? I expected it to work similarly as specifying 'osc build --jobs N' on the command line, but looking in the logs of a remote build server, it see that it actually runs with a higher number '+ /usr/bin/make -O VERBOSE=1 -j8'. Is there a way to limit the requested number of parallel build jobs in the _constraints file, or is the only way to put this in the spec file like '%cmake_build --jobs 4'? [1] https://openbuildservice.org/help/manuals/obs-user-guide/cha.obs.build_job_c...