Adds text with highlighted words to visualization.

        Args:
             exp: list of tuples [(id, weight), (id,weight)]
             label: label id (integer)
             div_name: name of div object to be used for rendering(in js)
             exp_object_name: name of js explanation object
             text: if False, return empty
             opacity: if True, fade colors according to weight

def visualize_instance_html(self, exp, label, div_name, exp_object_name,
                                text=True, opacity=True):
        """Adds text with highlighted words to visualization.

        Args:
             exp: list of tuples [(id, weight), (id,weight)]
             label: label id (integer)
             div_name: name of div object to be used for rendering(in js)
             exp_object_name: name of js explanation object
             text: if False, return empty
             opacity: if True, fade colors according to weight
        """
        if not text:
            return u''
        text = (self.indexed_string.raw_string()
                .encode('utf-8', 'xmlcharrefreplace').decode('utf-8'))
        text = re.sub(r'[<>&]', '|', text)
        exp = [(self.indexed_string.word(x[0]),
                self.indexed_string.string_position(x[0]),
                x[1]) for x in exp]
        all_occurrences = list(itertools.chain.from_iterable(
            [itertools.product([x[0]], x[1], [x[2]]) for x in exp]))
        all_occurrences = [(x[0], int(x[1]), x[2]) for x in all_occurrences]
        ret = '''
            %s.show_raw_text(%s, %d, %s, %s, %s);
            ''' % (exp_object_name, json.dumps(all_occurrences), label,
                   json.dumps(text), div_name, json.dumps(opacity))
        return ret