This document describes how cmark-gfm was packaged for build2. In particular, this understanding will be useful when upgrading to a new upstream version. The upstream package contains libcmark-gfm and libcmark-gfm-extensions libraries and the cmark-gfm program. Currently, we only package libraries and package them separately. We add the upstream package as a git submodule and symlink the required files and subdirectories into the build2 package subdirectories. Then, when required, we "overlay" the upstream with our own header/source files. Note that symlinking upstream submodule subdirectories into a build2 package subdirectory results in creating intermediate build files (.d, .o, etc) inside upstream directory while building the package in source tree. That's why we need to make sure that packages do not share upstream source files via subdirectory symlinks, not to also share the related intermediate files. If several packages need to compile the same upstream source file, then only one of them can symlink it via the parent directory while others must symlink it directly. We also add the `ignore = untracked` configuration option into .gitmodules to make sure that git ignores the intermediate build files under upstream/ subdirectory. Normally, when packaging a cmake-based project, we try to deduce the source file and compilation/linking option sets analyzing the root and feature/component/platform-specific CMakeLists.txt and .cmake files. In practice, however, that can be uneasy and error prone, so you may also need to refer to cmake-generated configuration files or, as a last resort, to see the actual compiler and linker command lines in the build log. If that's the case, you can configure/build the upstream package on the platform of interest running the following commands in the project root directory. On POSIX and in MinGW shell: $ make VERBOSE=1 With MSVC: > nmake VERBOSE=1