withstand voltage of RS-485 Transceiver
The bullet item under FEATURES says:

-7V to +12V common-mode input voltage range

This range of voltages is mentioned many times in the tables describing the driver and receiver DC characteristics.
In other words, the receiver will work correctly (and the driver will not be overloaded) as long as both signal lines fall within this range, and the differential voltage between them is at least ±0.2 V.