code: function updateCritical(root, update) {
    var clonedRoot = root.clone();
    if (update.type === 'rule') {
      clonedRoot.append(clean(update.clone()));
    } else {
      update.clone().each(function (rule) {
        clonedRoot.append(clean(rule.root()));
      });
    }
    return clonedRoot;
  }
docs: Update a critical root.
  
  @param {Object} root Root object to update.
  @param {Object} update Update object.
  @return {Object} clonedRoot Root object.