code: func (q *QueryStringQuery) DefaultOperator(operator string) *QueryStringQuery {
  	q.defaultOperator = operator
  	return q
  }
docs: // DefaultOperator sets the boolean operator of the query parser used to
  // parse the query string.
  //
  // In default mode (OR) terms without any modifiers
  // are considered optional, e.g. "capital of Hungary" is equal to
  // "capital OR of OR Hungary".
  //
  // In AND mode, terms are considered to be in conjunction. The above mentioned
  // query is then parsed as "capital AND of AND Hungary".