code: def decode(self, buffer: bytes) -> tuple[int, int]:
      self._comment_spans = False
      if self.mode == "1":
          data = self._decode_bitonal()
          rawmode = "1;8"
      else:
          maxval = self.args[-1]
          data = self._decode_blocks(maxval)
          rawmode = "I;32" if self.mode == "I" else self.mode
      self.set_as_raw(bytes(data), rawmode)
      return -1, 0
  
imports: from __future__ import annotations
  import math
  from io import BytesIO
  from .None import Image, ImageFile
  from ._binary import i16be
  from ._binary import o8
  from ._binary import o32le
label_desc: Use image node_id 6 for calling the PpmPlainDecoder obj's underlying member method code with example usage: obj.decode(buffer) and returns: unknown,  int