code: def parse(cls, fptr, offset, length):
          
          # Must seek to end of box.
          nbytes = offset + length - fptr.tell()
          fptr.read(nbytes)
          return cls(length=length, offset=offset)
docs: Parse JPX free box.
  
          Parameters
          ----------
          f : file
              Open file object.
          offset : int
              Start position of box in bytes.
          length : int
              Length of the box in bytes.
  
          Returns
          -------
          FreeBox
              Instance of the current free box.