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?

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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.