HTML vs. XHTML - WHATWG WikiIt is the MIME type (which may or may not be determined by file extension) that determines what type of document you are using. Any document served as text/html, including a document authored with the intention of being XHTML, is technically an HTML document. Note that XHTML 1.0 previously defined that documents adhering to the compatibility guidelines were allowed to be served as text/html, but H
