class_docstr: A small helper class to read fields stored in JPEG2000 header boxes
  and to easily step into and read sub-boxes.
class_docstr_tok: ["A","small","helper","class","to","read","fields","stored","in","JPEG2000","header","boxes","and","to","easily","step","into","and","read","sub-boxes","."]
code: def __init__(self, fp, length=-1):
      self.fp = fp
      self.has_length = length >= 0
      self.length = length
      self.remaining_in_box = -1
  
imports: import io
  import os
  import struct
  from .None import Image, ImageFile, _binary
label_desc: Use image node_id 1 to create a new BoxReader object  with example: obj = BoxReader(fp, length)