Wrong examples in the rank feature query documentation

[rueian]

Hi, I noticed that the rank feature query documentation contains the following examples:

PUT /test/_doc/2?refresh
{
  ....
  "topics": {
    "sports": 35,
    "formula one": 65,
    "brazil": 20
  }
}

PUT /test/_doc/3?refresh
{
  ...
  "topics": {
    "movies": 60,
    "super hero": 65
  }
}

and the documentation states that users can boost the relevance scores by:

GET /test/_search
{
  "query": {
    "bool": {
      ...
      "should": [
        ...
        {
          "rank_feature": {
            "field": "topics.sports",
            "boost": 0.4
          }
        }
      ]
    }
  }
}

However, the documentation doesn't say that users can't boost scores by other multi term fields like "field": "topics.super hero" or "field": "topics.formula one"

I think it is better having some notices in the documentation about that not any arbitrary field name is supported by the rank_feature query.