code: function formCluster(params, callback) {
    var query = formQueryLib.createFormQuery(params);
    var q = {
      "search_request" : {
        _source : sourceFields.concat(['text']),
        sort : [
          { "visitors.@timestamp" : {"order" : "desc"}},
        ],
        size : querySize(params),
        query: query
      },
      "query_hint": "*",
      "algorithm": "lingo",
      "field_mapping": {
        "title": ["_source.title"],
        "content": ["_source.text"],
        "url": ["_source.uri"]
      }
    };
  
    doPost('/contentItem/_search_with_clusters', JSON.stringify(q), function(err, res) {
      if (err) {
        GLOBAL.error('formCluster, carrot2 extension not installed?', err, q);
        callback(err);
        return;
      }
      res.query = q;
      if (!res || res.hits.hits.length < 1) {
        GLOBAL.info('NO HITS FOR', JSON.stringify(q, null, 2));
      }
      // FIXME don't send text
      callback(err, res);
    });
  }
docs: Executes carrot2 cluster query