is quirks mode legit?

I was on vacation without access to my good friend Internet Explorer, and I threw together a pretty complete web app. When I got home, I was surprised and encouraged to see开发者_开发技巧 that my site was working in IE... until I threw in any sort of valid doctype. I know it isn't best practice to throw browsers into quirks mode, or it wouldn't be called quirks mode, but I guess my question is... what are the practical ramifications of having a 'quirks mode' site? Is it necessary or even worth it to painstakingly slave away to correct the issues of which I am yet unaware, or can I leave it as is, functioning cross browser? Thanks.

If your site renders wrong in standards mode, but correct in quirks mode, chances are it's errornous. Some current browsers may fix your mistakes even in standard mode, but you have no idea about what future browsers will do with it. With standards mode, you can be absolutely sure that a valid site that looks fine in modern browsers will show up correctly.

Browsers are more interoperable, i.e., have the same behavior as each other, in the no-quirks mode compared to the quirks mode. The no-quirks mode is what most Web standards people and browser developers care about and consider and test. So it's more likely that you run into differences between browsers in quirks mode.

For example, in quirks mode, the body fills the viewport in WebKit/Blink, but does not in Gecko (I'm not sure about Edge). In no-quirks mode, body height works the same in all browsers.

(There's one counter-example, though, where browsers agree in quirks mode but not in no-quirks mode: body being the "viewport scrolling element" for scrollTop etc.)

Some versions of IE (8 and 9?) deliberately had less features in their quirks modes (e.g. the canvas element). So if you care about IE and want to be able to use the features IE actually supports, just not in quirks mode, then that would be another reason to not use quirks mode.

Finally, and maybe obviously, you're likely to run into more "weird" behavior that is the quirks themselves, like color and some other stuff not inheriting into table elements, that top and bottom margins collapse more, IDs and classes being case-insensitive, and so on.

Declaring a proper doctype is technically required for HTML validation by W3; however, lots of people leave their code un-doctyped for browsers to use Quirks mode instead. I've done this many times and it usually works out fine; however, you run the risk of browsers not interpreting your code correctly.

In other words, the cross-browser functionality you speak of could very easily break down into cross-browser hell without valid doctype declarations.

A.k.a., it's up to you as to how robust your site needs to be.

Quirks mode typically is the browsers attempt at fixing your errors in order to render correctly, however it's important to remember that if your site renders in standards compliant mode it will likely render ok with future browsers (at least for the time being).