title: Elasticsearch highlighter number of tokens before and after
body: <p>I'm using the plain highlighter (Elasticsearch 5.2). Here is an example</p>
  
  <pre><code>PUT bookstore
  {
    "mappings": {
      "books": {
        "properties": {
          "list": {
            "properties": {
              "summary": {
                "type": "text"
              },
              "title": {
                "type": "text"
              }
            }
          }
        }
      }
    }
  }
  </code></pre>
  
  <hr>
  
  <pre><code>POST bookstore/books/1
  {
    "list": [
      {
        "summary": "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.",
        "title": "Elasticsearch"
      }
    ]
  }
  </code></pre>
  
  <hr>
  
  <pre><code>GET bookstore/books/_search
  {
    "query": {
      "simple_query_string": {
        "query": "scrambled"
      }
    },
    "highlight": {
      "fields": {
        "*": {
          "require_field_match": false,
          "number_of_fragments": 1,
          "fragment_size": 70
        }
      }
    }
  }
  </code></pre>
  
  <hr>
  
  <pre><code>"highlight": {
    "list.summary": [
      " &lt;em&gt;scrambled&lt;/em&gt; it to make a type specimen book. It has survived not only five"
    ]
  }
  </code></pre>
  
  <p>My question is, how can I make it to center the highlighted word? In this case the highlighted word is at the beginning, on other cases is at the end. How can I make sure that is in the middle? </p>
  
  <p>Ideally what I want is to specify number of tokens before and after the highlighted text, instead of fragment size.</p>