Silva 1.5 developer preview: interfaces

Hi there,

I'm writing documentation on developer changes in Silva 1.5. As probably 
already know, Silva 1.5 is the first release of Silva which will be 
using Zope 3 technologies in the Silva core, using Five. We've already 
been using Five for layout package and the like, but we're taking it a 
step further.

Here's the note I wrote on the new way interfaces work.

Zope 3 interfaces
-----------------

Silva now uses Zope 3 interfaces throughout, instead of Zope 2 interfaces.

If you use interfaces in your own code, import the `Interface` base 
class like
this::

   from zope.interface import Interface

Instead of using `__implements__`, state that your class implements
interfaces using the `implements` class annotation::

   from zope.interface import implements

   ...

   class Foo:
       implements(IFoo)

You can check whether an instance provides an interface (i.e. whether
its class implements an interface or the interface directly provides
an interface) using `providedBy` (in Zope 2 this used to be written
'isImplementedBy')::

   IFoo.providedBy(instance)

In the rare case you want to check whether a *class* implements an
interface (i.e. whether its instances will provide that instance), you
use `implementedBy` (this used to be `isImplementedByInstancesOf` in
Zope 2)::

   IFoo.implementedBy(some_class)