A very nice feature of CMake is that we build out-of-source, the build directory can be any directory, and it does not have to be a subdirectory of the project directory. This means that we can port a project to CMake while not intruding into the previous/present configuration and build mechanism. For the migration of a non-trivial project, it is very useful that CMake files can coexist with other build frameworks to allow a gradual migration, both in terms of options, features, and portability, and to allow the developer community to adapt to the new framework. To allow both traditional and CMake configurations to coexist for a while, a typical strategy is to collect all CMake code in CMakeLists.txt files and all auxiliary CMake source files under a cmake subdirectory. In our example, we will not introduce a cmake subdirectory, but rather keep auxiliary files closer to the targets and sources requiring them, but we will take care to keep almost all files used by the traditional Autotools build unmodified, with one exception: we will apply few modifications in order to place autogenerated files under the build directory and not in the source tree.