Genshi stream prior to rendering.
This will allow plugins like Tags to add form controls without completely
overriding the `WikiModule`.
There is also a utility Genshi filter `trac.util.html.expand_markup()` which
can be used to expand embedded `Markup()` events. This is useful if you wish
to manipulate the actual Wiki content, for example.
Thanks to Noah for doing most of the work at PyCon :)