docs: def sum_transactions(transactions):
      """ Sums transactions into a total of remaining vacation days. """
      workdays_per_year = 250
      previous_date = None
      rate = 0
      day_sum = 0
      for transaction in transactions:
          date, action, value = _parse_transaction_entry(transaction)
          if previous_date is None:
              previous_date = date
          elapsed = workdays.networkdays(previous_date, date, stat_holidays()) - 1
  
          if action == 'rate':
              rate = float(value) / workdays_per_year
          elif action == 'off':
              elapsed -= 1  # Didn't work that day
              day_sum -= 1  # And we used a day
          day_sum += rate * elapsed
  
          if action == 'days':
              day_sum = value  # Fixed value as of this entry
  
          previous_date = date
  
      return day_sum