This document will describe concepts used in site.js for content representation and structuring.
There are several type of pages in site.js
Document is ordinary page. Its content is inlined or external html code that will be embedded as-is.
Catalog is a structure that contains subpages. It's represents them as links list.
Feed is a structure that contains subpages as well. However it represents nested documents as feed - sequence of blocks where each contains subpage content.