Depends on what you mean. For me or you? Yes, it won't be easy, just like it won't be easy to write a complex parser and rendering engine. For them, the browser makers? It's pretty darn easy considering they already built the foundations. They just need to adhere to the standards which have been unchanged for so many years. I can only tag as total irresponsibility the fact a browser still comes out these days without FULL standards compliance.
And that goes or ALL browsers. Amaya included.