What does XHTML stand for?

XHTML stands for Extensible HyperText Markup Language. It is a W3C specification that reformulates HTML as an XML 1.0 application with stricter syntax rules.

Is XHTML still used today?

Yes, but mostly as XHTML5, the XML serialization of the HTML5 standard. Many sites still write XHTML-style markup, though most serve it as text/html for broad browser compatibility.

What is the MIME type for XHTML?

The official MIME type is application/xhtml+xml. Local files can also use the .xhtml or .xht extensions, which trigger XHTML mode in the browser without an HTTP header.

Can browsers display XHTML served as text/html?

Yes, but the browser parses it as HTML, not XML. The document is no longer treated as XHTML, so XML rules like fail-fast error handling and namespaces stop applying.

What is the difference between XHTML 1.0 Strict and Transitional?

Strict allows only modern structural elements and forbids presentational tags such as font and center. Transitional permits those legacy tags so that authors can migrate older HTML 4 pages without rewriting every block.

Does Internet Explorer support XHTML?

Internet Explorer 9, 10, and 11 support XHTML when the server sends application/xhtml+xml. Internet Explorer 5.5 through 8 do not support the MIME type and prompt the user to save the file to disk.

XHTML5 is the XML serialization of HTML5 defined inside the HTML Living Standard. Authors get HTML5 elements like video, canvas, and audio with the strict XML syntax rules of XHTML.

Should I use XHTML or HTML5 for new projects?

Use HTML5 for almost every new project. The HTML5 parser is forgiving, ships in every browser, and supports the same elements. Pick XHTML5 only when you need strict XML parsing or integration with XML toolchains.

What happens when an XHTML document has a parsing error?

The browser stops parsing at the first error and shows a yellow XML error message. No fix-up rules run, so a single missing closing tag or unencoded ampersand can break the entire page.

How do I convert HTML to XHTML?

Lowercase every element and attribute name, quote every attribute value, close every void element with a trailing slash, and add the xmlns declaration to the root html tag. Validate with the W3C Markup Validator before serving the file.

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XHTML: Browser Support, Features, vs HTML

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XHTML: Browser Support, Features, vs HTML

XHTML is the strict XML reformulation of HTML. Learn what XHTML is, which browsers support application/xhtml+xml, key features, and how it differs from HTML.

Prince Dewani

May 6, 2026

On This Page

About XHTML
Browser Support
Key Features
XHTML vs HTML
Serve XHTML
Deprecation
Citations

XHTML is a W3C reformulation of HTML in XML that requires lowercase tags, quoted attributes, and closed elements. Served with the application/xhtml+xml MIME type, it works in Chrome 4+, Edge 12+, Firefox 2+, Safari 3.1+, Opera 9+, Internet Explorer 9+, Samsung Internet 4+, and Android Browser 2.1+, but not in IE 5.5 to 8.

This guide covers what XHTML is, browser support, the key features, differences from HTML, how to serve it correctly, and whether XHTML is still used.

What is XHTML?

XHTML, short for Extensible HyperText Markup Language, is a W3C specification that reformulates HTML as an XML application. It uses the namespace http://www.w3.org/1999/xhtml and enforces strict syntax rules: lowercase elements, quoted attribute values, and a closing tag for every opening tag. Browsers parse it as XML rather than as forgiving HTML.

Which browsers does XHTML support?

Most modern browsers parse XHTML when the server sends it with the application/xhtml+xml MIME type. The exception is Internet Explorer 5.5 through 8, which prompts the user to download the file instead of rendering it.

Loading browser compatibility data...

XHTML compatibility in Chrome

Chrome supports XHTML from Chrome 4 on, on Windows, macOS, Linux, ChromeOS, and Android. Pages served with the application/xhtml+xml MIME type render in XML mode and stop rendering on the first parse error.

XHTML compatibility in Edge

Microsoft Edge supports XHTML from Edge 12 on across Windows, macOS, and Linux. Edge inherits Chromium's XML parser, so behavior matches Chrome on every platform Edge ships on.

XHTML compatibility in Firefox

Firefox supports XHTML from Firefox 2 on across Windows, macOS, Linux, and Android. Mozilla's Gecko engine was one of the first to ship application/xhtml+xml and continues to render the markup in strict XML mode.

XHTML compatibility in Safari

Safari supports XHTML from Safari 3.1 on macOS and from Safari 3.2 on iOS and iPadOS. The WebKit XML parser handles application/xhtml+xml the same way across iPhone, iPad, and Mac.

XHTML compatibility in Opera

Opera supports XHTML from Opera 9 on the desktop and from Opera Mobile 10. After Opera moved to the Chromium engine, the same XML parser used by Chrome handles XHTML content in current Opera builds.

XHTML compatibility in Samsung Internet

Samsung Internet supports XHTML from Samsung Internet 4 on Android. Built on Chromium, it parses application/xhtml+xml the same way Chrome does and applies the same fail-fast error handling.

XHTML compatibility in Android Browser

The Android Browser supports XHTML from Android 2.1 on. Modern Android phones now use Chrome or a Chromium WebView, which inherits the same XML parsing behavior across the entire platform.

XHTML compatibility in Internet Explorer

Internet Explorer supports XHTML only from IE 9 on Windows. IE 5.5 to IE 8 did not support application/xhtml+xml and instead prompted the user to save the response to disk. Microsoft has retired Internet Explorer, so the supported window is IE 9 to IE 11.

Note: XHTML behavior shifts across browsers and OS, especially on legacy IE and older Safari. Test it on real browsers and OS with TestMu AI. Try TestMu AI free!

What are the key features of XHTML?

XHTML keeps the element set of HTML 4 but tightens parsing in several ways:

Well-formed XML: Every document must parse as valid XML. A single missing closing tag or stray ampersand stops rendering and shows an error message.
Lowercase tags and attributes: All element names and attribute names must use lowercase, and attribute values must be wrapped in single or double quotes.
Closed tags for every element: Void elements like br, img, and hr need an explicit self-closing slash, written as br /, img /, and hr /.
XML namespace declaration: The root html element must declare xmlns="http://www.w3.org/1999/xhtml" so the parser knows which language it is reading.
Fail-fast error handling: Browsers stop parsing on the first XML error and show a yellow error screen, unlike HTML's permissive recovery.
Polyglot markup option: XHTML 1.0 documents can be served as either text/html or application/xhtml+xml, which lets the same file work in older HTML-only browsers.
XML toolchain compatibility: Because XHTML is valid XML, standard XML parsers, XSLT processors, and validators can read and transform the markup directly.

What is the difference between XHTML and HTML?

XHTML is a stricter, XML-based form of HTML. The two languages share most elements but differ in syntax, parsing rules, and how browsers handle errors. The table below shows the practical differences a developer or QA engineer needs to know.

Dimension	HTML	XHTML
Parser	HTML parser, lenient	XML parser, strict
Tag case	Mixed case allowed	Lowercase only
Attribute quotes	Optional in some cases	Mandatory on every value
Empty elements	br, img, hr	br /, img /, hr /
Error handling	Browser tries to recover	Stops on the first error
MIME type	text/html	application/xhtml+xml
Namespace	Not required	xmlns="http://www.w3.org/1999/xhtml"
document.write	Works	Throws an error

How do you serve XHTML with the correct MIME type?

XHTML is only XHTML when the server sends it with the right Content-Type header. Adding a DOCTYPE alone does not switch the browser into XML mode. Follow these steps to serve a page as true XHTML:

Set the Content-Type header: Configure your server (Apache, NGINX, Express, IIS) to return Content-Type: application/xhtml+xml on the HTTP response for the document.
Add the XML declaration: Place the line that declares XML 1.0 with UTF-8 encoding at the very top of the file, before the DOCTYPE.
Declare the namespace on the root element: Use html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" as the opening tag so the parser recognizes the document language.
Save local files with .xhtml or .xht: For files opened from disk, browsers detect the type from the extension and switch to the XML parser without an HTTP header.
Verify the response: Open browser DevTools, switch to the Network tab, refresh the page, and confirm the Type column shows application/xhtml+xml on the document request.

A minimal XHTML page that follows every rule looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Sample XHTML Page</title>
  </head>
  <body>
    <h1>Hello, XHTML</h1>
    <p>Every tag is lowercased, quoted, and properly closed.</p>
    <br />
    <img src="logo.png" alt="Logo" />
  </body>
</html>

If the browser shows the source code as plain text or strips the XML declaration, the server is still sending text/html. Fix the Content-Type header before debugging anything else.

Is XHTML deprecated?

XHTML is not formally deprecated, but it has been overtaken by HTML5. The W3C halted XHTML 2.0 development and superseded the XHTML 1.0 Recommendation, pointing authors to the HTML Living Standard. XHTML5 lives on as the XML serialization of HTML5, so authors who want strict syntax can still write XHTML5 and serve it as application/xhtml+xml.

In my experience, most production sites send their pages as text/html now, even when the markup follows XHTML rules, because the HTML5 parser handles both styles without any server configuration. New projects should pick HTML5 unless an XML toolchain forces the XHTML5 serialization.

Citations

All XHTML version numbers, MIME type rules, and platform notes in this guide come from these primary sources:

MDN Web Docs - XHTML glossary: developer.mozilla.org/en-US/docs/Glossary/XHTML
Wikipedia - XHTML: en.wikipedia.org/wiki/XHTML
W3C - XHTML 1.0 Specification: w3.org/TR/xhtml1
W3C - XHTML FAQ: w3.org/MarkUp/2004/xhtml-faq
W3C - XHTML Media Types Note: w3.org/2003/01/xhtml-mimetype
W3C - Serving HTML and XHTML: w3.org/International/articles/serving-xhtml
WHATWG - HTML Living Standard, parsing: html.spec.whatwg.org/multipage/parsing.html
Microsoft Learn - XHTML in IE9 archive: learn.microsoft.com/archive/blogs/ie/xhtml-in-ie9
IETF - RFC 3236, the application/xhtml+xml media type: ietf.org/rfc/rfc3236.txt
IANA - application/xhtml+xml media type registry: iana.org/assignments/media-types/application/xhtml+xml
WebKit blog: webkit.org/blog
Mozilla Hacks blog: hacks.mozilla.org

Author

Prince Dewani

Blogs: 8

Prince Dewani is a Community Contributor at TestMu AI, where he manages content strategies around software testing, QA, and test automation. He is certified in Selenium, Cypress, Playwright, Appium, Automation Testing, and KaneAI. Prince has also presented academic research at the international conference PBCON-01. He further specializes in on-page SEO, bridging marketing with core testing technologies. On LinkedIn, he is followed by 4,300+ QA engineers, developers, DevOps experts, tech leaders, and AI-focused practitioners in the global testing community.