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 has 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.