Translates and adds the escape sequence.

        :param idx: Provides the ending index of the escape sequence.
        :param char: The actual character that was escaped.

def add_escape(self, idx, char):
        """
        Translates and adds the escape sequence.

        :param idx: Provides the ending index of the escape sequence.
        :param char: The actual character that was escaped.
        """

        self.fmt.append_text(self.fmt._unescape.get(
            self.format[self.str_begin:idx], char))