The Canon EOS Rebel T4i's body is very similar to the T3i's; the biggest difference is on the inside, with the new hybrid sensor. The sensor has the usual set of nine phase-detection autofocus sensors in the center, but adds a larger set of contrast-detection AF sensors around them for use with the new STM lenses, like the 18-135mm f3.5-5.6 shown here. The lenses include a stepper motor for silent AF operation during movie shooting. Support for contrast AF allows them to perform continuous AF during movie capture as well.
The 40mm lens is so thin there's barely room for the AF/MF switch on the barrel. Personally, I'd rather have it be larger with OIS, as it seems silly to intentionally work to make a lens this thin on such a large body.