class_docstr: Basic message object.
  
  A message object is defined as something that has a bunch of RFC 2822
  headers and a payload.  It may optionally have an envelope header
  (a.k.a. Unix-From or From_ header).  If the message is a container (i.e. a
  multipart or a message/rfc822), then the payload is a list of Message
  objects, otherwise it is a string.
  
  Message objects implement part of the `mapping' interface, which assumes
  there is exactly one occurrence of the header per message.  Some headers
  do in fact appear multiple times (e.g. Received) and for those headers,
  you must use the explicit API to set or get all the headers.  Not all of
  the mapping methods are implemented.
code: def __contains__(self, name):
      return name.lower() in [k.lower() for k, v in self._headers]
  
imports: import re
  import uu
  import binascii
  import warnings
  from cStringIO import StringIO
  import email.charset
  from email import utils
  from email import errors
label_desc: Use image node_id 16 for calling the Message obj's underlying member method code with example usage: obj.__contains__(name) and returns: unknown