Which HTML DocType?
doctype, html
Solution
While `<!doctype html>` is perfectly fine, the WHAT-WG recommendation is to use `<!DOCTYPE html>`, just in case you end up serving the document as XHTML5 (in which case the capitalisation becomes important).
@David Dorward (unable to comment yet, so…) I disagree with your representation of HTML5. While the new stuff (structural elements etc) are presently poorly supported by browsers, HTML5 is 90% HTML4 with defined error handling (finally). Browsers parse HTML5 the same as HTML4, so assuming you don’t use structural elements (`div` still works) the differences are minimal. Validator.nu gives better results than W3’s HTML4.1 Strict validator, is being more rapidly developed, and is based on a more detailed spec.
My advice would be to ignore the new things in HTML5 for the moment and treat it as a more precise spec for HTML4. There are no disadvantages and several benefits.
Problem
I was asked today by a senior developer which doctype I'd use if I was going to write something (personal / non-commercial) for the open web. I responded, `<!doctype html>`, to which I was greeted with a look of shock, horror and surprise and then asked to explain myself. To my mind, it's a good candidate because current browsers (IE, FF, Opera, Safari) will look at it and switch the content into standards mode - even though they don't implement HTML5. If I want to actually take advantage of HTML5 elements, I can use some javascript to create a reference to those tags not recognised by, say, IE (e.g. `document.createElement('article');`) and then work with them as if they were native parts of the DOM. Was this really such a bad answer? What would you have answered and why?