code: func NewHistogramVec(opts HistogramOpts, labelNames []string) *HistogramVec {
  	desc := NewDesc(
  		BuildFQName(opts.Namespace, opts.Subsystem, opts.Name),
  		opts.Help,
  		labelNames,
  		opts.ConstLabels,
  	)
  	return &HistogramVec{
  		metricVec: newMetricVec(desc, func(lvs ...string) Metric {
  			return newHistogram(desc, opts, lvs...)
  		}),
  	}
  }
docs: // NewHistogramVec creates a new HistogramVec based on the provided HistogramOpts and
  // partitioned by the given label names.