The html parser spec defines what every sequence of bytes should parse into. It defines certain such sequences as containing "errors", but it still defines exac

The html parser spec defines what every sequence of bytes should parse into. It defines certain such sequences as containing "errors", but it still defines exactly how they should be parsed. There is no invalid html. Every browser follows the spec, so every browser will parse the same html to the same thing. This is true even if the html contains "errors". The only checking most html receives is to make sure it renders correctly in a browser. If you are writing your own parser, you likely want it to do the same thing as every browser. In that case, you should use a parser that conforms to the spec.