At least in firefox this isn't handled as XML DOM document (they might still use the XML parser). XHTML pages used to be. On your page: document instanceof X

At least in firefox this isn't handled as XML DOM document (they might still use the XML parser). XHTML pages used to be. On your page: document instanceof XMLDocument // false On https://upload.wikimedia.org/wikipedia/commons/e/e9/SVG-Grundelemente.svg https://upload.wikimedia.org/wikipedia/commons/e/e9/SVG-Grun... document instanceof XMLDocument // true