Not sure why you're being downvoted. WebKit actually implements the WHATWG HTML parsing algorithm [1], and so do Trident [2] and Gecko [3]. The W3C HTML 4 spec

Not sure why you're being downvoted. WebKit actually implements the WHATWG HTML parsing algorithm [1], and so do Trident [2] and Gecko [3]. The W3C HTML 4 spec didn't waste a word on parsing and simply referred to SGML [4], which (for very good reasons) no relevant browser actually implemented. Obviously, browser developers did some crazy/remarkable things before the WHATWG came along, but a lot of credit for today's lenient HTML parsing certainly belongs with the WHATWG. [1] https://webkit.org/blog/1273/the-html5-parsing-algorithm/ https://webkit.org/blog/1273/the-html5-parsing-algorithm/ [2] https://blogs.msdn.microsoft.com/ie/2011/07/06/html5-parsing-in-ie10/ https://blogs.msdn.microsoft.com/ie/2011/07/06/html5-parsing... [3] https://hacks.mozilla.org/2010/05/firefox-4-the-html5-parser-inline-svg-speed-and-more/ https://hacks.mozilla.org/2010/05/firefox-4-the-html5-parser... [4] https://www.w3.org/TR/html4/conform.html#h-4.2 https://www.w3.org/TR/html4/conform.html#h-4.2