title: When do you use React-Router getChildRoutes?
body: <p>I'm confused about how and when you can use <code>getChildRoutes</code> because it's part of <code>PlainRoute</code>. How do you access <code>PlainRoute</code> in the first place? So instead of building <code>&lt;Route&gt;</code> components I can use <code>&lt;PlainRoute&gt;</code>s and then inside the component it was rendering it will have getChildRoutes? What does <code>partialNextState</code> refer to?</p>