These two pages:
http://www.digitalmars.com/d/1.0/function.html
http://www.digitalmars.com/d/2.0/function.html

there is a text:
... Covariant return types are supported ....
    ^^^^^^^^^^^^^^^^^^^^^^

that point to non-existing page:
http://www.digitalmars.com/d/1.0/covariant and
http://www.digitalmars.com/d/2.0/covariant respectively.

Wouldn't like to create a new bug report, bugzilla is full of them already...
Besides, it's really trivial to fix.