[html5] Validator.nu’s (X)HTML5 Validator does not validate XHTML5

Mon Aug 28 08:57:43 PDT 2017

When I choose either of the XML options, it changes the text field to:

  <?xml version="1.0" encoding="UTF-8"?>
  <!DOCTYPE html>
  <

And says:

  Fatal Error: Illegal processing instruction target (found xml)
  At line 2, column 5
  ↩<?xml version="1.0"

For testing, I copied and pasted the source of my home page:
http://www.chaosreigns.com/
Which has had a link at the bottom to verify its XHTML5 via validator.nu
for 8 years - which still works:
https://html5.validator.nu/?doc=http://www.chaosreigns.com/

On 08/28, Domenic Denicola wrote:
> Click "More options" then look under "Parser".
> 
> -----Original Message-----
> From: Help [mailto:help-bounces at lists.whatwg.org] On Behalf Of Jorge .
> Sent: Monday, August 28, 2017 12:05
> To: help at lists.whatwg.org
> Subject: [html5] Validator.nu’s (X)HTML5 Validator does not validate XHTML5
> 
> Validator.nu (X)HTML5 Validator at https://html5.validator.nu validates only HTML5, not XHTML5, despite its name, when attempting to do so via direct input (Text Field).
> 
> Tested with this markup:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <!DOCTYPE html>
> <html xmlns="http://www.w3.org/1999/xhtml">
>    <head>
>       <meta charset="UTF-8"/>
>       <title>My title</title>
>    </head>
>    <body>
>    </body>
> </html>
> 
> The submission form does not have an option to forcibly request XHTML5 validation instead of HTML5. Even when the markup is preceded by the XML declaration (which nevertheless is purportedly not necessary if contents are UTF-8), the validator reports the very declaration as an
> error:
> 
> > Error: Saw <?. Probable cause: Attempt to use an XML processing 
> > instruction in HTML. (XML processing instructions are not supported in 
> > HTML.)
> 
> revealing that even with such markup it is validating HTML5 instead of XHTML5.
> 
> The generic validator at https://validator.nu used to have a preset or parser (cannot remember) specifically for XHTML5, but not anymore either it seems.
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