Support XHTML5 (XML serialization of HTML5)

[Nils Fredrik Gjerull]

Frameworks and libraries that generate html should output well-formed html that can be used for both HTML serialization (text/html) and XML serialization (application/xhtml+xml). This implies that Django should continue to output XML compatible markup even for HTML5.

This do not mean that Django need to be restricted by the XHTML-Transitional and XHTML-Strict standard. It only means that HTML5 needs to be written in a XML compatible style.

This affects Django in three ways:

1. HTML must be well-formed. All start-tags needs an end-tag (except self-closing tags). This is already the case.
2. All self-closing tags must end with '/>'.
3. All boolean attributes must have a value e.g 'checked="checked"'.

I will say that this time is the best time ever to serve pages with application/xhtml+xml, because all browsers supports it. IE was the road blocker for year, but since IE9 it supports it as well. Se a list of the ​default value of the Accept header for various browsers from Mozilla.

See:

• ​https://www.w3.org/TR/html/introduction.html#html-vs-xhtml
• ​https://www.w3.org/TR/html/the-xhtml-syntax.html
• ​https://en.wikipedia.org/wiki/HTML5#XHTML_5_(XML-serialized_HTML_5)

[Tim Graham]

The ​django-developers discussion hasn't yielded a consensus to make this change. As I said on the mailing list, please look into ​custom widget templates for this.