Refs and the DOM: clarify when ref callbacks are invoked (#1069)

content/docs/refs-and-the-dom.md

@@ -251,7 +251,7 @@ class CustomTextInput extends React.Component {
 }
 ```
 
-React will call the `ref` callback with the DOM element when the component mounts, and call it with `null` when it unmounts. `ref` callbacks are invoked before `componentDidMount` or `componentDidUpdate` lifecycle hooks.
+React will call the `ref` callback with the DOM element when the component mounts, and call it with `null` when it unmounts. Refs are guaranteed to be up-to-date before `componentDidMount` or `componentDidUpdate` fires.
 
 You can pass callback refs between components like you can with object refs that were created with `React.createRef()`.