Once again, we leveraged the power of add_custom_target to add an arbitrary build target to our build system. In this case, the documentation will be built using Sphinx. Since Sphinx is a Python program that can be extended with other Python modules, the docs target will depend on the Python interpreter. We make sure that dependencies are satisfied by using find_package. Note that the FindSphinx.cmake module is not yet a standard CMake module; a copy of it is included with the project source, under the cmake subdirectory.