Why is it so hard to make a fully HTML CSS compliant web browser?

[GWestphal]

To my knowledge not a single browser is 100% standard compliant. Why is that? Why is there so much variance over how HTML gets rendered and why isn't it being done "right" in all cases.

 

[Markbnj]

Because the CSS rules are very complex and they are constantly getting more so.

 

[EagleKeeper]

Hard to hit a moving target

 

[GWestphal]

Well with HTML5 I would agree is hasn't been standardized completely, but HTML4 had a standardized version, didn't it?

 

[Aldon]

I don't know for sure, but if all of these browser would be the same then there wouldn't be a point in competing against each other. Just my thoughts on this.

 

[Savatar]

Check out this article for a few points about why, even if there was a 'standard', there still would be problems and browsers which behaved differently or supported different features: http://www.impressivewebs.com/no-standards-compliant-browser/

Also, several years ago different browsers did things different way... and many browsers still try to support webpages which were designed using legacy markup / those special one-off tags: http://superuser.com/questions/303433/why-is-internet-explorer-not-a-standards-compliant-browser

It is getting better, by far, with newer browsers, but there are still quirks (one example is with mobile browsers doing things weird, like handling position:fixed funny until newer versions b/c they didn't think there was space for fixed elements).

 

[Cogman]

When it comes to HTML4 and CSS2, most modern browsers are really pretty decent. IE came a long way to standards conformance with 9+. Unless you are doing something on the fringe of the standard, you are pretty safe.

HTML5, however, is a different beast entirely. Unfortunately, I think that the standards committee is to blame here. It is currently understood that there will be no HTML6, so HTML5 has become a standards dumping ground. Sadly, what gets into the standard seems to be more driven by what the majority of browser vendors implement and less on what would make a good standard.

IMO we are going to see HTML5 become a PDF like standard, it will include everything. Unfortunately, I don't think there will be anyone who fully implements the standard, just whatever bits and pieces tickle their fancy or are commonly used.

 

[Markbnj]

It's because you can do this:

http://codepen.io/i0z/pen/mFLCw

 

[Leros]

CSS is turing complete

http://jsfiddle.net/Camilo/eQyBa/

 

[Aluvus]

There are multiple inter-related standards (HTML, CSS, JavaScript) which are themselves problematic. CSS especially is complex, with many moving parts that interact in not-always-obvious ways, complicated edge cases, no reference implementation, and dense "standard-ese" writing. The standards are written by distinct groups of people (who have changed considerably over time) and have not always been built with a lot of thought for how they would interact with each other, or prior versions of themselves.

Legacy issues have been especially problematic; supporting markup targeted at old browser implementations, usually with a "quirks mode", requires a lot of guesswork and creates a lot of issues. Behaviors that become common before a spec is written or while it is being written may become de facto parts of the spec even if they are poorly designed or badly defined.

There can also be perverse incentives to do things wrong. IE had a hell of a time updating to better match the standards after so many businesses had built a dependency on the quirks of IE 6. Smaller browsers have consistently fought with the issue that if their bigger competitors do something wrong, but popular websites rely on the wrong behavior, the smaller browsers look "broken" to users.

Well with HTML5 I would agree is hasn't been standardized completely, but HTML4 had a standardized version, didn't it?

Define "standardized", I guess. There is an HTML 5 spec in draft right now, and most of the big battles are probably over. Part of the issue there is that what people commonly call "HTML 5" is far more than HTML 5 per se; for example, the details of the canvas element (which draws in SVG, another spec) or how to handle the video element (preferred codecs, DRM support, on and on).

There are multiple variants of HTML 4.01 (Strict, Transitional/"Loose", Frameset), in addition to XHTML 1.0/1.1 (again: Strict, Transitional/"Loose", Frameset) which came out at essentially the same time.

I don't know for sure, but if all of these browser would be the same then there wouldn't be a point in competing against each other. Just my thoughts on this.

They can still compete on other features - performance, additional capabilities, UI quality, etc. Until recently, Safari and Chrome both used the same WebKit rendering engine and behaved very similarly in rendering pages. Google has since created their own fork (called Blink) for Chrome. Multiple browsers have used the Gecko (Mozilla/Firefox) and Trident (IE) engines.