This article is in need of a technical review.
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HTML5 and HTML/XHTML
The HTML5 standard defines both these syntaxes. The choice of syntax is indicated by the MIME type (which is sent in the HTTP
Content-Type header): the MIME type for HTML syntax is
text/html, and the MIME type for XHTML syntax is
This example shows an HTML document and an XHTML document including the relevant HTTP headers:
HTTP/1.1 200 OK Content-Type: text/html <!DOCTYPE html> <html lang=en> <head> <meta charset=utf-8> <title>HTML</title> </head> <body> <p>I am a HTML document</p> </body> </html>
HTTP/1.1 200 OK Content-Type: application/xhtml+xml <html xml:lang="en" xmlns="
http://www.w3.org/1999/xhtml"> <head> <title>XHTML</title> </head> <body> <p>I am a XHTML document</p> </body> </html>
MIME type versus DOCTYPE
Before HTML5, the two syntaxes were defined by two separate specifications: HTML 4.01 and XHTML 1.0. According to the XHTML1 standard, you could use XHTML by declaring a special DOCTYPE. However, no browsers have ever implemented this, and the HTML5 standard has reversed the decision. If your page is sent as
text/html, you are not using XHTML.
Instead, the proper MIME type must be present in the
Content-Type HTTP header. If you only put the MIME type into an HTML meta tag like
<meta http-equiv=…>, it will be ignored and treated like
If you serve your pages as
text/html and believe that you are writing XHTML, you may face several problems, as described in these articles:
- No to XHTML an excellent article from Spartanicus
- Beware of XHTML by David Hammond
- Sending XHTML as text/html Considered Harmful by Ian Hickson
- XHTML's Dirty Little Secret by Mark Pilgrim
- XHTML - What's the Point? by Henri Sivonen
- XHTML is not for Beginners by Lachlan Hunt
Most modern browsers support XHTML, including Firefox, Chrome, Safari, Opera, and Internet Explorer (since IE 9). (Internet Explorer 8 and older browsers instead show a download dialog box for unknown file types when they see an XHTML document with the correct XHTML MIME type.)
Differences from HTML