'Add a file to the given MHTML collection.
Args:
location: The original location (URL) of the file.
content: The binary content of the file.
content_type: The MIME-type of the content (if available)
transfer_encoding: The transfer encoding to use for this file.'

def add_file(self, location, content, content_type=None, transfer_encoding=E_QUOPRI):

    self._files[location] = _File(content=content, content_type=content_type, content_location=location, transfer_encoding=transfer_encoding)
