Breaking: #72492 - Removed XHTML2 support¶
See Issue #72492
The support for XHTML2 documents in the TYPO3 Frontend has been removed.
The TypoScript option
config.doctype = xhtml_2 has no effect anymore.
Any TYPO3 instance using XHTML2 for frontend rendering.
Disable all header code and set your own doctype.