docs: function generateLocaleExtra(locale, localeData) {
    const dayPeriods = getDayPeriodsNoAmPm(localeData);
    const dayPeriodRules = getDayPeriodRules(localeData);
  
    let dayPeriodsSupplemental = [];
  
    if (Object.keys(dayPeriods.format.narrow).length) {
      const keys = Object.keys(dayPeriods.format.narrow);
  
      if (keys.length !== Object.keys(dayPeriodRules).length) {
        throw new Error(`Error: locale ${locale} has not the correct number of day period rules`);
      }
  
      const dayPeriodsFormat = removeDuplicates([
        objectValues(dayPeriods.format.narrow),
        objectValues(dayPeriods.format.abbreviated),
        objectValues(dayPeriods.format.wide)
      ]);
  
      const dayPeriodsStandalone = removeDuplicates([
        objectValues(dayPeriods['stand-alone'].narrow),
        objectValues(dayPeriods['stand-alone'].abbreviated),
        objectValues(dayPeriods['stand-alone'].wide)
      ]);
  
      const rules = keys.map(key => dayPeriodRules[key]);
  
      dayPeriodsSupplemental = [...removeDuplicates([dayPeriodsFormat, dayPeriodsStandalone]), rules];
    }
  
    return `${HEADER}
  const u = undefined;
  
  export default ${stringify(dayPeriodsSupplemental).replace(/undefined/g, 'u')};
  `;
  }