Projects can be configured in a nested manner, by configuring a project as a subproject of another project. This allows for documentation projects to share a search index and a namespace or custom domain, but still be maintained independently.
For example, a parent project, Foo is set up with a subproject, Bar. The
documentation for Foo will be available at:
https://foo.readthedocs.io/en/latest/
The documentation for Bar will be available under this same path:
https://foo.readthedocs.io/projects/bar/en/latest/
In the admin dashboard for your project, select "Subprojects" from the menu. From this page you can add a subproject by typing in the project slug.
Projects and subprojects can also be used to share a custom domain with a number of projects. To configure this, one project should be established as the parent project. This project will be configured with a custom domain. Projects can then be added as subprojects to this parent project.
If the example project Foo was set up with a custom domain,
docs.example.com, the URLs for projects Foo and Bar would
respectively be at: http://docs.example.com/en/latest/ and
http://docs.example.com/projects/bar/en/latest/
Projects that are configured as subprojects will share a search index with their parent and sibling projects. This is currently the only way to share search indexes between projects, we do not yet support sharing search indexes between arbitrary projects.