How is @sys.ignore assigned to Dialogflow entity

Question

In exported json files of Dialogflow agent I noticed that my training phrase is split into 2 json objects and one of them has @sys.ignore meta property. I know that entity can be defined as system entity starting with @sys. but I don't know what @sys.ignore is and how can it be assigned or unassigned

Example of intent with training phrase split:

"data": [
  {
    "text": "cleaning of ",
    "userDefined": false
  },
  {
    "text": "machine part",
    "meta": "@sys.ignore",
    "userDefined": false
  }

I also checked here https://dialogflow.com/docs/reference/system-entities

and here

https://cloud.google.com/dialogflow-enterprise/docs/reference/system-entities
but no luck

Answer 1

I had the same query and I followed up with Dialogflow team for the same, here the response from them:

@sys.ignore is used to ignore matches from the ML with entities. @sys.ignore may have been added while you were editing your training phrases and removing a highlighted phrase or word.

So, @sys.ignore will force Dialogflow to prevent it from getting matched to any of the entities.
In my experience, it is generally added when Dialogflow annotates some entity in the training phrases and I manually removes it.

Hope it helps.