There are many articles and resources out there that preach about XHTML versus HTML and various DOCTYPEs and their uses (a list to a couple of those articles is at the bottom of this post). But regardless of the reasons and arguments for either side, it is very clear that transitional DOCTYPES are better than strict ones for WordPress blogs.
Strict DOCTYPEs are…well, too strict. They don’t allow for certain (necessary) tags to remain in your WordPress blog. Tags such as
are used by WordPress to drop a line through text. Using a Strict DOCTYPE with this is impossible; you will receive an error. Time and time again I see this while reviewing WordPress themes and plugins. It doesn’t need to happen.
Changing Your Doctype in WordPress Under the Presentation tab click on Header. Find the following selection of code: