The posts will be researched and go through multiple drafts for professionalism before posting. In this hope, it will strive to enable discussion that isn't flaming and collective of the topic at hand. For as much as I can achieve at my level of writing skill and researching the topic at hand.

He he goes through the purpose of the posts, the areas he's going to focus on, some about the theory that will be used, and the implementation and documentation he'll provide through the series.

The post itself are really just notes to support the content in the podcast, but they provide plenty of information by themselves. They talk about what interfaces are, include examples of both them and a class (showing how they differ) and an example of a class using and interface (dog implementing animal).

There are also a few other notes there at the bottom mentioning the purpose of interfaces, which one to choose when, and two miscellaneous notes about how interfaces can help both you and your code.

Inner Classes are contained in parent classes and offer a sort of namespace mechanism for the public and open private class data transfer for private subclasses.

The functionality is already available in other languages, but the question is whether it is needed in PHP. The short answer is no. With PHP execution model, it would further slow down and bloat PHP compilation.

He demonstrates their purpose with some simple examples but also gives the reasons why it would be a bad thing to try to include them, including the better choice of namespaces over inner classes.