phrase

multiobjective.Metric.phrase(delta, better)

Full clause describing a change in this metric, e.g. “average journey time is 0.2 minutes worse”.

Override by passing phrasing – a callable taking (metric, delta, better) and returning a full clause – for metrics where the generic “improves by / is worse by” wording reads awkwardly (e.g. counts of people, rather than continuous measures).