code: function createEnterARButton (clickHandler) {
    var arButton;
  
    // Create elements.
    arButton = document.createElement('button');
    arButton.className = ENTER_AR_BTN_CLASS;
    arButton.setAttribute('title', 'Enter AR mode.');
    arButton.setAttribute('aframe-injected', '');
  
    arButton.addEventListener('click', function (evt) {
      document.getElementsByClassName(ENTER_AR_BTN_CLASS)[0].style.display = 'none';
      document.getElementsByClassName(EXIT_AR_BTN_CLASS)[0].style.display = 'inline-block';
      clickHandler();
    });
    return arButton;
  }
docs: Creates a button that when clicked will enter into stereo-rendering mode for AR.
  
  Structure: <div><button></div>
  
  @param {function} enterARHandler
  @returns {Element} Wrapper <div>.