code: func (a *DateHistogramAggregation) Interval(interval string) *DateHistogramAggregation {
  	a.interval = interval
  	return a
  }
docs: // Interval by which the aggregation gets processed.
  // Allowed values are: "year", "quarter", "month", "week", "day",
  // "hour", "minute". It also supports time settings like "1.5h"
  // (up to "w" for weeks).