code: def GetFormatSpecification(self):
      
      format_specification = specification.FormatSpecification(
          self.type_indicator)
  
      # FAT volume header signature.
      format_specification.AddNewSignature(b'\x55\xaa', offset=510)
  
      if definitions.PREFERRED_NTFS_BACK_END == self.TYPE_INDICATOR:
        # NTFS file system signature.
        format_specification.AddNewSignature(b'NTFS    ', offset=3)
  
      # HFS boot block signature.
      format_specification.AddNewSignature(b'LK', offset=0)
  
      # HFS master directory block signature.
      format_specification.AddNewSignature(b'BD', offset=0)
  
      # HFS+ file system signature.
      format_specification.AddNewSignature(b'H+', offset=1024)
  
      # HFSX file system signature.
      format_specification.AddNewSignature(b'HX', offset=1024)
  
      # Ext file system signature.
      format_specification.AddNewSignature(b'\x53\xef', offset=1080)
  
      # ISO9660 file system signature.
      format_specification.AddNewSignature(b'CD001', offset=32769)
  
      # YAFFS file system signature.
  
      return format_specification
docs: Retrieves the format specification.
  
      Returns:
        FormatSpecification: format specification or None if the format cannot
            be defined by a specification object.