// Attempts to open a section and navigate to a different sub-page.
  var openSection = new OpenSectionTransition(section);
  var changeSubpage = openSection.finished.then(function() {
    // After opening the section, navigate to another sub-page.
    return new ChangeSubpageTransition(subpage);
  }, function() {
    // Apparently openSection was canceled due to another router event; do nothing.
  });