[wiki] CMake_Useful_Variables's description of CMAKE_SOURCE_DIR seems wrong
https://cmake.org/Wiki/CMake_Useful_Variables
CMAKE_SOURCE_DIR
this is the directory, from which cmake was started, i.e. the top level source directory
from which cmake was started
For out-of-source builds (which are as far as I know recommended mode for CMake) it seems to be not the case, as cmake typically getting started with build directory as current directory.