Docs: warn about custom domains on subprojects
@@ -15,7 +15,7 @@ The documentation for ``Bar`` will be available under this same path:
https://foo.readthedocs.io/projects/bar/en/latest/
-Adding a Subproject
+Adding a subproject
-------------------
In the admin dashboard for your project, select "Subprojects" from the menu.
@@ -26,7 +26,7 @@ Subproject aliases
You can use an alias for the subproject when it is created. This allows you to override the URL that is used to access it, giving more configurability to how you want to structure your projects.
-Sharing a Custom Domain
+Sharing a custom domain
-----------------------
Projects and subprojects can also be used to share a custom domain with a number
@@ -39,6 +39,18 @@ If the example project ``Foo`` was set up with a custom domain,
respectively be at: https://docs.example.com/en/latest/ and
https://docs.example.com/projects/bar/en/latest/
+Custom domain on subprojects
+----------------------------
+
+Adding a custom domain to a subproject is allowed,
+but your documentation will always be served from
+the domain of the parent project.
+
+For example, if the domain of a parent project is ``https://docs.example.com``,
+and you add the ``https://subproject.example.com/`` domain to one of its subprojects,
+it will always redirect to the domain of the parent project
+``https://docs.example.com/projects/subproject/``.
+
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