<no title> — Cabal 3.16.1.0 User's Guide

A field of this type is always optional because it defaults to empty, which corresponds to the root directory of the repository and is the same as specifying `.` explicitly.

Some projects put the sources for multiple packages inside a single VCS repository. This field lets you specify the relative path from the root of the repository to the top directory for the package, i.e. the directory containing the package’s `.cabal` file.