The SIO pins are tolerant to input voltages higher than the IO supply voltage. The Hot swap feature prevents input from being clamped to the IO supply level, when the input voltage is above the IO supply voltage. Each SIO pin can tolerate any input voltage up to 5.5V, regardless of IO supply voltage.
For cases where the input voltage exceeds IO supply voltage, the DC input leakage current is < 100uA. This feature allows the SIO to be connected to an external bus that can be switched to voltage levels higher than the IO supply voltage.