I need to make my mind clear about HTML doctypes. in this page: http://kovo.intl.uk.to I add breadcrumbs navigation using RDFa. but then page was no more valid. I googled and I found out to change doctype to:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
Now the page is 100% valid, but what means XHTML and such LOW number? At my webpages I am using HTML 4.01 strict due I write pages mostly in Slovak for Slovak people and what I see on some computers and how they are used is "stone age" (Windows XP + ie8 in better case :D).
Is this correct solution and what affects have doctypes to users or search engines ?