Comment by bazoom42

But not closing <p> etc has always been valid HTML. Back from SGML it was possible for closing tags to be optional (depending on the DTD), and Netscape supported this from the beginning.

Leaving out closing tags is possible when the parsing is unambigous. E.g <p>foo<p>bar is unambiguous becuse p elements does not nest, so they close automatically by the next p.

The question about invalid HTML is a sepearate issue. E.g you can’t nest a p inside an i according to the spec, so how does a browser render that? Or lexical error like illegal characters in a non-quoted attribute value.

This is where it gets tricky. Render anyway, skip the invalid html, or stop rendering with an error message? HTML did not specify what to do with invalid input, so either is legal. Browsers choose to go with the “render anyway” approach, but this lead to different outputs in different browsers, since it wasn’t agreed upon how to render invald html.

The difference between Netscape and IE was that Netscape in more cases would skip rendering invalid HTML, where IE would always render the content.