/** The key of the configuration. e.g. 4 */
    String QUERY_COLLAPSE_MAX_CONCURRENT_GROUP_RESULTS = "query.collapse.max.concurrent.group.results";

    /** The key of the configuration. e.g. similar_docs */
    String QUERY_COLLAPSE_INNER_HITS_NAME = "query.collapse.inner.hits.name";

    /** The key of the configuration. e.g. 0 */
    String QUERY_COLLAPSE_INNER_HITS_SIZE = "query.collapse.inner.hits.size";