Describing UI structures

JSX is the best way to describe complex UI structures. Let's look at some JSX markup that declares a more elaborate structure than a single paragraph:

import React from 'react'; 
import { render } from 'react-dom'; 
 
// This JSX markup describes some fairly-sophisticated 
// markup. Yet, it's easy to read, because it's XML and 
// XML is good for concisely-expressing hierarchical 
// structure. This is how we want to think of our UI, 
// when it needs to change, not as an individual element 
// or property. 
render(( 
  <section> 
    <header> 
      <h1>A Header</h1> 
    </header> 
    <nav> 
      <a href="item">Nav Item</a> 
    </nav> 
    <main> 
      <p>The main content...</p> 
    </main> 
    <footer> 
      <small>&copy; 2016</small> 
    </footer> 
  </section> 
  ), 
  document.getElementById(&apos...