What is the meaning of bits 31 and 30 in an SEH exception code?

I'm trying to find out what the bits mean in an SEH exception code. I found out that bit 28 is reserved by the system for system-defined exceptions from MSDN's article on RaiseException. However, given the excep开发者_运维问答tion code 0xC0000005, I can't discover why it is not 0x00000005. Is the bit pattern 0xC0000000 indicative of something not lost to the mists of time? If so, what is it?

From the "Raising Software Exceptions" page on MSDN:

These two bits describe the basic status of the code:
11 = error, 00 = success, 01 = informational, 10 = warning.