This fixes WCAG 2.0 compliance because we were already using HTML5 markup.
The strict XML headers setting never worked for production servers, developers
used browser validators for compliance testing. XHTML 5 option is relatively
similar to this obsolete option, but still it can not be used on production servers.
XHTML Strict 1.x was a standardised dead end, HTML5 is the new de-facto-standard
supported by all major browsers including latest versions of IE.
Please note nothing changes in our coding style because HTML5 is a superset of
several previous standards, it is recommended to use only features that are
already implemented in all our supported browsers.
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