Difference of _NSIG between the kernel UAPI header and libc header

[Xi Ruoyao]

Hi,

In the kernel UAPI header, _NSIG is defined with the same value of
SIGRTMAX; but in the libc header, _NSIG is defined as SIGRTMAX + 1.

I'm wondering: what is the rationale of the difference here?

-- 
Xi Ruoyao <xry111@xry111.site>