Highlighting Lines in Codes

Particular lines of codes can be highlighted by adding {:pre data-line="[line#3],[line#6]-[line#8]"} just before a code-block.

For example:

{:pre data-line="4-8,11,14-15"}
```cpp
int
main()
{
    asio::io_context ioc;
    auto exec = ioc.get_executor();

    auto in = asio::posix::stream_descriptor(exec, ::dup(STDIN_FILENO));
    auto out = asio::posix::stream_descriptor(exec, ::dup(STDOUT_FILENO));

    async_copy_all(in, out, [](auto&& ec, auto total){
        std::cout << "\ntransferred " << total << " bytes\n";
        if (ec.failed())
        {
            std::cerr << "transfer failure: " << ec.message() << std::endl;
            std::exit(ec.value());
        }
    });

    ioc.run();

    return 0;
```

This is how the above one will be rendered like: