Typo in ch 6

[bcstrongx]

The question is from the following description in Smcdeleg/Ssccfg specification:

For sampling usages, the OS will initialize a counter with a large positive value
suitably close to overflow, and clear the associated event selector overflow (OF) bit
via sireg3/sireg4.

However, the specification also states that: illegal instruction exceptions are raised when attempts to access sireg3 or sireg6.

Is this a typo, or do I miss something ?