private static SpannableStringBuilder AppendSpan(this SpannableStringBuilder mutableString, ISpan span)
        {
            switch (span)
            {
            case TextSpan textSpan:
                mutableString.AppendNormalText(textSpan);
                break;

            case ProjectSpan projectSpan:
                mutableString.AppendProjectText(projectSpan);
                break;

            case TagSpan tagSpan:
                mutableString.AppendTagText(tagSpan);
                break;
            }

            return(mutableString);
        }