class _Regex(BaseFilter):
        """
        Filters updates by searching for an occurrence of ``pattern`` in the message text.
        The ``re.search`` function is used to determine whether an update should be filtered.
        Refer to the documentation of the ``re`` module for more information.
        Note:
            Does not allow passing groups or a groupdict like the ``RegexHandler`` yet,
            but this will probably be implemented in a future update, gradually phasing out the
            RegexHandler (See `Github Issue
            <https://github.com/python-telegram-bot/python-telegram-bot/issues/835/>`_).
        Examples:
            Use::
                MessageHandler(Filters.regex(r'help'), callback)
            to capture all messages that contain the word help. You can also use::
                MessageHandler(Filters.regex(re.compile(r'help', re.IGNORECASE), callback)
             if you want your pattern to be case insensitive. This approach is recommended
             if you need to specify flags on your pattern.
        Args:
            pattern (:obj:`str` | :obj:`Pattern`): The regex pattern.
        """