code: function moreLikeThis(uris, callback) {
    // FIXME use all URIs
    var uri = uris[0];
    retrieveByURI(uri, function(err, res) {
      if (err) {
        callback(err);
        return;
      }
      var mlt = require('./moreLikeThis.js');
      var content = utils.getTextFromHtml(res._source.content);
  
      mlt.fields = sourceFields;
      mlt.query.bool.should[0].mlt_field.content.like_text = content;
      mlt.query.bool.should[1].mlt_field.title.like_text = res._source.title;
      var data = JSON.stringify(mlt);
  
      doPost('/contentItem/_search', data, callback);
    });
  }
docs: more like this field api