and VS 2017 uses toolset version v141 which is still "14".
At the time the VS 2017 generator was first written we were using a
VS 15 preview and its toolset was still called v140. Please submit
a MR to update the above-linked docs to mention that MSVC14 is for
v140 or v141.
> I wonder how I could detect the v141(_xp) toolset?
Use CMAKE_C_COMPILER_VERSION instead. The `MSVC##` variables are legacy,
though not deprecated because they can still be handy due to the
"or another compiler that simulates it" part of the documentation.