function IsWellFormedUnitIdentifier(unit) {
      unit = toLowerCase(unit);
      if (IsSanctionedSimpleUnitIdentifier(unit)) {
          return true;
      }
      var units = unit.split('-per-');
      if (units.length !== 2) {
          return false;
      }
      var numerator = units[0], denominator = units[1];
      if (!IsSanctionedSimpleUnitIdentifier(numerator) ||
          !IsSanctionedSimpleUnitIdentifier(denominator)) {
          return false;
      }
      return true;
  }
https://tc39.es/ecma402/#sec-iswellformedunitidentifier
@param unit