Breaking: #97927 - Removed TypoScript option config.doctypeSwitch¶
Previous TYPO3 versions allowed to set
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.
Setting the option
config.doctypeSwitch has no effect anymore, the
XML declaration and doctype statement are kept as is.
TYPO3 installations with old templates having this TypoScript option set.
It is recommended to avoid using this functionality, and to switch to HTML5.