We'll start by familiarizing ourselves with a fundamental React terminology. It will help us build a clear picture of what the React library is made of. This terminology will most likely update over time, so keep an eye on the official documentation at http://facebook.github.io/react/docs/glossary.html.

Just like the DOM is a tree of nodes, React's virtual DOM is a tree of React nodes. One of the core types in React is called ReactNode. It's a building block for a virtual DOM, and it can be any one of these core types:

ReactElements and ReactTexts are ReactNodes. An array of ReactNodes is called a ReactFragment. You will see examples of all of these in this chapter.

Let's start with an example of...