SAR ADC DAC Question
If a DAC is used as part of a SAR ADC, then we don't already know the value of the MSB. The logic in the ADC makes an assumption about the value of the MSB, uses the DAC to create an analog voltage corresponding to that assumption, and then the comparator determines whether the actual input voltage is higher or lower than the DAC output. At that point, the SAR logic (of which the comparator is a part) makes the decision about whether the MSB should be high or low. The wording of the sentence you quote could be improved a bit, but in the context of SAR ADCs it is pretty obvious.