code: public StructuredQueryDefinition containerQuery(ContainerIndex index, StructuredQueryDefinition query) {
      checkQuery(query);
      return new ContainerQuery(index, query);
    }
docs: Matches a query within the substructure contained by an element or JSON property.
  @param index    the element or JSON property
  @param query    the query over the contained substructure
  @return    the StructuredQueryDefinition for the container query