[johncmouser]

would you need the doctype if the user-agent said it was html5 compliant?

[pzmarzly]

Without doctype, browsers will render your page in quirks mode, leaving you scratching your head because of margins being set out of nowhere.

https://developer.mozilla.org/en-US/docs/Mozilla/Mozilla_qui...

[SahAssar]

The doctype is required for it to be a valid html5 document.

[recursive]

Yes. Especially then. Without a doctype, it's not html5.