The fastest way to confirm that a given HTML document is not valid XML is to change the HTTP Content-Type from "text/html" to "application/xhtml+xml". Here is

The fastest way to confirm that a given HTML document is not valid XML is to change the HTTP Content-Type from "text/html" to "application/xhtml+xml". Here is what I know about using XHTML in practice: https://www.nayuki.io/page/practical-guide-to-xhtml https://www.nayuki.io/page/practical-guide-to-xhtml