Thanks for pointing this out.
I've changed the documentation to use the "ref" attribute.
(Interestingly, there are five JUnit tests with separate configuration files that all correctly use "ref". It seems like the docs have had this mistake from the beginning.)

Fixed in revision 1555091.
Please verify and close.

Note to the team:
Perhaps this attribute should be AppenderRef instead of ref.
The code changes to do this seem fairly straightforward, but this may break existing configurations. At this point the documentation is simply wrong so I'm just fixing the documentation.

I would vote for whatever is consistent with the rest of the configuration schema.

(Reopening issue)
Now that we are talking about coming out of beta on the mailing list, perhaps now is the best time to change this attribute from "ref" to "AppenderRef".

I'll change the docs back to "AppenderRef".
I'll change the implementation to accept either "AppenderRef" or (for backwards compatibility) "ref". If both are specified, AppenderRef wins.

Hmm... Perhaps I was too enthusiastic there...

After taking another good look, using ref (and not AppenderRef) may be the most consistent.
For reference, Root and Logger config elements look like this:

    <Root level="info">
      <AppenderRef ref="RollingFile"/>
    </Root>

Compare to the Route config element:

    <Routing name="Routing">
      <Routes pattern="$${sd:type}">
        ...
        <Route ref="AuditLogger" key="Audit"/>
      </Routes>
    </Routing>

So it looks like just fixing the documentation was the correct thing to do and there is no need for further code changes.
I will mark this issue as 'fixed' again. Sorry for the confusion.

Hi Remko,
Thanks for the quick update and your enthusiastic. We need such kind of review and thinking to understand the case better.
This issue could be closed after the manual on website updated.
And as a junior developer, thanks again for the high quality code to learn from. : )

Hongdi, thank you for bringing it to our attention.