message: Add some comments explaining how we are using aria-hidden property to
  hide content outside of the BaseDialog to screen reader users.
diff: @@ -50,14 +50,19 @@ export default React.createClass({
  },
  componentDidMount: function() {
  + // Retrieve the root node of the Riot application outside the dialog
  this.applicationNode = document.getElementById('matrixchat');
  if (this.applicationNode) {
  + // Hide the content outside the dialog to screen reader users
  + // so they won't be able to navigate into it and act on it using
  + // screen reader specific features
  this.applicationNode.setAttribute('aria-hidden', 'true');
  }
  },
  componentWillUnmount: function() {
  if (this.applicationNode) {
  + // When dismissing the dialog, make all of Riot available to screen reader users again
  this.applicationNode.setAttribute('aria-hidden', 'false');
  }
  },
  