docs: def format_outpat(outpat, xn):
      """
      Format an outpat for the given transaction.
  
      Format the given output filename pattern.  The pattern should
      be a format string with any combination of the following named
      fields:
  
      ``year``
        The year of the transaction.
      ``month``
        The month of the transaction, with leading zero for
        single-digit months.
      ``fy``
        The financial year of the transaction (being the year in
        which the financial year of the transaction *ends*).
        A financial year runs from 1 July to 30 June.
      ``date``
        The date object itself.  The format string may specify
        any attribute of the date object, e.g. ``{date.day}``.
        This field is deprecated.
      """
      return outpat.format(
          year=str(xn.date.year),
          month='{:02}'.format(xn.date.month),
          fy=str(xn.date.year if xn.date.month < 7 else xn.date.year + 1),
          date=xn.date
      )