code: @GwtIncompatible("incompatible method")
      public static long getFragmentInSeconds(final Calendar calendar, final int fragment) {
          return getFragment(calendar, fragment, TimeUnit.SECONDS);
      }
docs: <p>Returns the number of seconds within the
  fragment. All datefields greater than the fragment will be ignored.</p>
  
  <p>Asking the seconds of any date will only return the number of seconds
  of the current minute (resulting in a number between 0 and 59). This
  method will retrieve the number of seconds for any fragment.
  For example, if you want to calculate the number of seconds past today,
  your fragment is Calendar.DATE or Calendar.DAY_OF_YEAR. The result will
  be all seconds of the past hour(s) and minutes(s).</p>
  
  <p>Valid fragments are: Calendar.YEAR, Calendar.MONTH, both
  Calendar.DAY_OF_YEAR and Calendar.DATE, Calendar.HOUR_OF_DAY,
  Calendar.MINUTE, Calendar.SECOND and Calendar.MILLISECOND
  A fragment less than or equal to a SECOND field will return 0.</p>
  
  <ul>
  <li>January 1, 2008 7:15:10.538 with Calendar.MINUTE as fragment will return 10
  (equivalent to calendar.get(Calendar.SECOND))</li>
  <li>January 6, 2008 7:15:10.538 with Calendar.MINUTE as fragment will return 10
  (equivalent to calendar.get(Calendar.SECOND))</li>
  <li>January 6, 2008 7:15:10.538 with Calendar.DAY_OF_YEAR as fragment will return 26110
  (7*3600 + 15*60 + 10)</li>
  <li>January 16, 2008 7:15:10.538 with Calendar.MILLISECOND as fragment will return 0
  (a millisecond cannot be split in seconds)</li>
  </ul>
  
  @param calendar the calendar to work with, not null
  @param fragment the {@code Calendar} field part of calendar to calculate
  @return number of seconds within the fragment of date
  @throws IllegalArgumentException if the date is <code>null</code> or
  fragment is not supported
  @since 2.4