I am trying to add some custom attribute using formatText. What I have tried so far:

    var Parchment = Quill.import('parchment');
    var commentAttributor = new Parchment.Attributor.Attribute('comment', 'comment', { 
        scope: Parchment.Scope.INLINE
    });
    Quill.register(commentAttributor, true);

and the delta looks like this:

"ops": [
  {
    "insert": "aa"
  },
  {
    "attributes": {
      "comment": "abc",
      "action": true
    },
    "insert": "aaaaaa"
  },
  {
    "insert": "aaa"
  },
  {
    "attributes": {
      "storyblock": true
    },
    "insert": "\n"
  },
  {
    "insert": "\n"
  }
]

However, when I restored the data from delta, the attribute is gone... what am i doing wrong here?