Leica M 240 + Zeiss ZM lenses
There is a hard key on the lens mount that brings up pairs of frames on the M4-P ... M9 : 28/90,50/75 and 35/135.
This should still work fine on uncoded lenses.
It could be refined further for coded lenses to only display one frame out of the pair.
It's the same mechanical keying and frameline mechanism that's been in the M since the M3. Nothing different about the new M other than an LED illuminator rather than the ambient light pipe. The paired framelines are the result of the framelines masks, nothing else, so the codings mean nothing with respect to the framelines.
The lens code influences what goes into the EXIF data and whether the data system in the camera applies lens corrections to the image data, that's all.
Thank you, both. Of course: there's no electronic communication between the camera body and the lens. Lost my head there for a moment.