var text = new RichText(
  text: new TextSpan(
    // Note: Styles for TextSpans must be explicitly defined.
    // Child text spans will inherit styles from parent
    style: new TextStyle(
      fontSize: 14.0,
      color: Colors.black,
    ),
    children: [
      new TextSpan(text: 'Hello'),
      new TextSpan(text: 'World', style: new TextStyle(fontWeight: FontWeight.bold)),
    ],
  ),
 );