code: def chunk_acTL(self, pos, length):
      s = ImageFile._safe_read(self.fp, length)
      self.im_custom_mimetype = "image/apng"
      return s
  
imports: import logging
  import re
  import struct
  import zlib
  from .None import Image, ImageFile, ImagePalette
  from ._binary import i8, i16be, i32be, o16be, o32be
  from ._util import py3
label_desc: Use image node_id 17 for calling the PngStream obj's underlying member method code with example usage: obj.chunk_acTL(pos, length) and returns: s