code: func NewExplainService(client *Client) *ExplainService {
  	return &ExplainService{
  		client:         client,
  		typ:            "_doc",
  		xSource:        make([]string, 0),
  		xSourceExclude: make([]string, 0),
  		fields:         make([]string, 0),
  		xSourceInclude: make([]string, 0),
  	}
  }
docs: // NewExplainService creates a new ExplainService.