private void start(Editable output, Object mark) {
        int len = output.length();
        output.setSpan(mark, len, len, Spannable.SPAN_MARK_MARK);

        if (HtmlTextView.DEBUG) {
            Log.d(HtmlTextView.TAG, "len: " + len);
        }
    }
Mark the opening tag by using private classes
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/html/HtmlTagHandler.java