def __init__(self, subscription_substitution_tag=None):
self._subscription_substitution_tag = None<EOL>if subscription_substitution_tag is not None:<EOL><INDENT>self.subscription_substitution_tag = subscription_substitution_tag<EOL><DEDENT>
Create a SubscriptionSubstitutionTag object

        :param subscription_substitution_tag: A tag that will be replaced with
                                              the unsubscribe URL. for example:
                                              [unsubscribe_url]. If this
                                              parameter is used, it will
                                              override both the text and html
                                              parameters. The URL of the link
                                              will be placed at the
                                              substitution tag's location,
                                              with no additional formatting.
        :type subscription_substitution_tag: string, optional