docs: def age(dt, now=None, add_direction=True, date_threshold=None):
      """
      :param dt: :class:`datetime<datetime.datetime>` instance to format
  
      :param now: :class:`datetime<datetime.datetime>` instance to compare to `dt`
  
      :param add_direction: if `True`, will add "in" or "ago" (example for `en`
         locale) to time difference `dt - now`, i.e "in 9 min." or " 9min. ago"
  
      :param date_threshold: above threshold, will use a formated date instead of
         elapsed time indication. Supported values: "day".
      """
      # Fail silently for now XXX
      if not dt:
          return ""
  
      if not now:
          now = datetime.datetime.utcnow()
  
      locale = babel.get_locale()
      dt = utc_dt(dt)
      now = utc_dt(now)
      delta = dt - now
  
      if date_threshold is not None:
          dy, dw, dd = dt_cal = dt.isocalendar()
          ny, nw, nd = now_cal = now.isocalendar()
  
          if dt_cal != now_cal:
              # not same day
              remove_year = dy == ny
              date_fmt = locale.date_formats["long"].pattern
              time_fmt = locale.time_formats["short"].pattern
              fmt = locale.datetime_formats["medium"]
  
              if remove_year:
                  date_fmt = date_fmt.replace("y", "").strip()
                  # remove leading or trailing spaces, comma, etc...
                  date_fmt = re.sub("^[^A-Za-z]*|[^A-Za-z]*$", "", date_fmt)
  
              fmt = fmt.format(time_fmt, date_fmt)
              return babel.format_datetime(dt, format=fmt)
  
      # don't use (flask.ext.)babel.format_timedelta: as of Flask-Babel 0.9 it
      # doesn't support "threshold" arg.
      return format_timedelta(
          delta,
          locale=locale,
          granularity="minute",
          threshold=0.9,
          add_direction=add_direction,
      )