AD5271 Confirm the datasheet

Hello, ADI team.

My customer considering to use AD5271. He has the doubt to datasheet described. In datasheet p19, Table11,

command7 , there is no description of the D3 is in error.To determine from Table 13 and 14, it seems like the need to select 1 in the part of DB3(C3) when writting to the command register.

What kind of the reason is that this part has become a X "especially don't care" in Table 11?