This document outlines different approaches for adding React to a WordPress theme or plugin, including using a CDN, Create-React-App, or a custom implementation. It distinguishes between a "brainless" CMS that uses WordPress to serve the front-end including React, and a "headless" CMS with no WordPress front-end and a separate JavaScript application. A "brainless" approach is good for adding smaller dynamic functionality, while a "headless" one allows for a completely decoupled architecture useful for building single-page applications.