void encode(std::string& data) {
    std::string buffer;
    buffer.reserve(data.size());
    for(size_t pos = 0; pos != data.size(); ++pos) {
        switch(data[pos]) {
            case '&':  buffer.append("&");       break;
            case '\"': buffer.append(""");      break;
            case '\'': buffer.append("'");      break;
            case '<':  buffer.append("&lt;");        break;
            case '>':  buffer.append("&gt;");        break;
            default:   buffer.append(&data[pos], 1); break;
        }
    }
    data.swap(buffer);
}