Not only it triggers standards mode, but that's the sole purpose of this declaration in HTML5 (well, strictly speaking you might want to use it for something el

Not only it triggers standards mode, but that's the sole purpose of this declaration in HTML5 (well, strictly speaking you might want to use it for something else, but that may not be the best idea). If you serve your document with application/xhtml+xml you can omit it — this MIME type itself triggers standards mode so doctype becomes redundant.