CSE HTML Validator

roedygr wrote:<span lang="de"> would engage a German dictionary. It does not.

roedygr wrote:What is the new feature?

The common way to serve HTML is with the MIME type 'text/html', but XHTML5 must be served with the MIME type 'application/xhtml+xml'. This creates problems for older browsers like IE8, so developers may not want to serve documents with 'application/xhtml+xml' to the general public. Fortunately IE9 added support for 'application/xhtml+xml', but that still leaves a lot of older browsers, like IE8 and below, that don't support 'application/xhtml+xml'.

'Polyglot' documents can be served with either 'text/html' or 'application/xhtml+xml', without any changes to the document itself (only the MIME type differs). This is because polyglot XHTML5 documents follow the rules for both HTML5 and XHTML5 documents and thus can be parsed by both HTML and XML parsers. Polyglot documents also result in the same DOM, whether parsed by an HTML parser or by an XML parser. This ensures that CSS and JavaScript work the same, regardless of the parser.