class_docstr: Generates output from a Message object tree.
  
  This basic generator writes the message to the given file object as plain
  text.
code: def _make_boundary(cls, text=None):
      # Craft a random boundary.  If text is given, ensure that the chosen
      # boundary doesn't appear in the text.
      token = random.randrange(sys.maxsize)
      boundary = ("=" * 15) + (_fmt % token) + "=="
      if text is None:
          return boundary
      b = boundary
      counter = 0
      while True:
          cre = cls._compile_re(
              "^--" + re.escape(b) + "(--)?$", re.MULTILINE
          )
          if not cre.search(text):
              break
          b = boundary + "." + str(counter)
          counter += 1
      return b
  
imports: import re
  import sys
  import time
  import random
  from copy import deepcopy
  from io import StringIO, BytesIO
  from email.utils import _has_surrogates
label_desc: Use image node_id 16 for calling the Generator obj's underlying member method code with example usage: obj._make_boundary(cls, text) and returns: b, boundary