> Collections allow you to define a new type of document that behave like Pages or Posts do normally, but also have their own unique properties and namespace.

It took me a while to parse this sentence. What about minimizing it, such as:

> Collections allow you to define documents that behave like Pages or Posts, but also have their own unique properties and namespace. You can iterate over your site's unique collections just like you can with Pages and Posts.

Kind of lame on the last sentence, but I wanted to draw a closer parallel between P & P + C.