Breaking: #97927 - Removed TypoScript option config.doctypeSwitch 

See forge#97927

Description 

Previous TYPO3 versions allowed to set config.doctypeSwitch via TypoScript.

If this option was set, the order of <?xml...> and <!DOCTYPE...> during the rendering of a Frontend page was reversed. This was needed in the past for Internet Explorer to be standards-compliant with XHTML. Otherwise IE's "Quirks Mode" was used.

Nowadays, usages for both Internet Explorer (which is not supported anymore) and XHTML have been low, which is why the option is now removed from TYPO3 Core.

Impact 

Setting the option config.doctypeSwitch has no effect anymore, the XML declaration and doctype statement are kept as is.

Affected installations 

TYPO3 installations with old templates having this TypoScript option set.

Migration 

It is recommended to avoid using this functionality, and to switch to HTML5.