I find this sentence really weird as it seems that a PID with 0 **is** possible when the kernel boots, starting a `sched` process with a 0 PID value (http://www.unix.com/solaris/90574-job-has-pid-0-a.html)

What about: `# Default value. A PID which value is 0 is not available when a Unix is started, meaning CR is not running in this case.`