This is annoying, I can't make Github expand to the line I need. I have a question about this text:

    Your controller can expect the ``$id`` parameter as well as the
    ``$contentDocument`` as we set a content on the route. The content could be
    used to define an intro section that is the same for each project or other
    shared data. If you don't need content, you can just not set it in the
    document.

Where is says "we set a content on the route", what does this mean? A content document? Some content? I would like to update this if possible.