User:Thisismyrofl/Template:Foo-no-doc

Suppose this is a template in the Template: namespace, named Template:Foo-no-doc. The page Documentation:Template:Foo-no-doc doesn't exist, nor does Template:Foo-no-doc/doc, so it automatically displays a warning: everything in green. Ideally, the green box is not coded for on the page, it just appears. However, this automatically-included warning (and indeed, any documentation that might be written) certainly would not be transcluded onto any host pages!

If instead this were a template in the User: or Project: namespace, the warning would not appear, because documentation is not expected there.