code: def next(self, start):
          
          position = start
          while True:
              # skip over any non-\xFF bytes
              position = self._offset_of_next_ff_byte(start=position)
              # skip over any \xFF padding bytes
              position, byte_ = self._next_non_ff_byte(start=position+1)
              # 'FF 00' sequence is not a marker, start over if found
              if byte_ == b'\x00':
                  continue
              # this is a marker, gather return values and break out of scan
              marker_code, segment_offset = byte_, position+1
              break
          return marker_code, segment_offset
docs: Return a (marker_code, segment_offset) 2-tuple identifying and
          locating the first marker in *stream* occuring after offset *start*.
          The returned *segment_offset* points to the position immediately
          following the 2-byte marker code, the start of the marker segment,
          for those markers that have a segment.