As ATU alluded, bit-of-word is handled as part of a more generalized system of casting. It is quite powerful and you would do well to familiarize yourself with it.
However...the simple answer is ':' followed by the bit number. Works with any numeric block...but not on struct fields. So V12:10 or D100:30 are both valid, but T0.Acc:0 is not.
Another useful place for info on casting is the Element Browser's Cast Builder. It's hidden under the 'More >>' button.