How do you set the parent attribute on a project within a repo manifest?

[Thomas Thorne]

In the manifest-format.txt file it states:

Attribute `name`: A unique name for this project.  The project's
name is appended onto its remote's fetch URL to generate the actual
URL to configure the Git remote with.  The URL gets formed as:
  ${remote_fetch}/${project_name}.git
where ${remote_fetch} is the remote's fetch attribute and
${project_name} is the project's name attribute.  The suffix ".git"
is always appended as repo assumes the upstream is a forest of
bare Git repositories.  If the project has a parent element, its
name will be prefixed by the parent's.

Is the use of "parent" here talking about Git-submodules only?  

I am using Phabricator to host a git repository and it liked to prepend repo URLs with the repo "Callsign" so the URL ends up being git://phabricator.example.com/diffusion/CS/repo-name.git which kind of breaks using a single remote for multiple projects.  

Is there a better way to prepend the callsign onto the repository fetch path than naming the project name="CS/repo-name.git"?  
When I do that it looks like it kind of works based on most of the config files.  I have not got the repository to clone yet but I expect that is a phabricator configuration issue rather than a repo one.