Does using an HTML 5 Doctype cause Quirks mode in modern browsers, since HTML5 isn't out yet?
(That is Modern Browsers were out before HMTL5 started spreading, so they don't properly support it.)
If yes, does this mean that the HTML 5 Doctype is tentatively like none at all?
EDIT: If not, what does it do in browsers that don't support and the like?
No it doesn't, see this article.
What's nice about this new DOCTYPE, especially, is that all current browsers (IE, FF, Opera, Safari) will look at it and switch the content into standards mode - even though they don't implement HTML5. This means that you could start writing your web pages using HTML5 today and have them last for a very, very, long time.
According to Wikipedia table (that I love) HTML 5 DOCTYPE triggers full standard mode for:
FF, Chrome, Opera 7.5+, Safari, Konqeror 3.5+ and also IE8!!!
and triggers Almost standard mode [*] for:
IE6 and IE7
So it's definitely the best DOCTYPE ever created!
"One DOCTYPE to bring them all and in the darkness bind them..." [Lords of the rings]
[*] "Almost standards" does NOT make such a big difference to full standard mode, in the same Wikipedia link above you can find more details.