function keyboardShortcutHandler_(e) {
    // Toggle CRT screen flicker.
    if ((e.ctrlKey || e.metaKey) && e.keyCode == 83) { // crtl+s
      container_.classList.toggle('flicker');
      output('<div>Screen flicker: ' +
             (container_.classList.contains('flicker') ? 'on' : 'off') +
             '</div>');
      e.preventDefault();
      e.stopPropagation();
    }
  }
Handler for keyboard shortcuts

@param {Event} e The click event