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                <section id = "app"></section>




                const Header = (props) => {
  return (
      {props.subtitle && <h2>{props.subtitle}</h2>}

Header.defaultProps = {
  title: 'Default title'

ReactDOM.render(<Header />, document.getElementById('app'));
//ReactDOM.render(<Header title="A new title" subtitle="An actual subtitle"/>, document.getElementById('app'));

// so, go ahead and remove the comments and switch the render call.
// in the current render call nothing in passed into the props and so
// the defaults are shown = "default title" and no subtitle.
// When we switch the render call = a title and subtitled are passed in through 
// props and are rendered to the screen.