What is kill-0 pid used for?

http://blog.csdn.net/pecywang/article/details/8558968

Group of colleagues talking about kill-0, talents, do not know what to do, look up the Internet, the special record as follows

The kill-0 PID does not send any signals, but the system will check for errors.
So it is often used to check whether a process exists, exists to return 0, and does not exist to return 1

Man Handbook:

The signals listed below May is available for use with kill. When known constant, numbers and default behavior are shown.
Name Num Action Description
0 0 N/A exit code indicates if a signal may sent