4 A field of this type is always optional because it defaults to empty, which
5 corresponds to the root directory of the repository and is the same as
6 specifying ``.`` explicitly.
8 Some projects put the sources for multiple packages inside a single VCS
9 repository. This field lets you specify the relative path from the root of the
10 repository to the top directory for the package, i.e. the directory containing
11 the package's ``.cabal`` file.