TYPO3 Core

###FORM_URL### is filled by typoLink_URL() while ###THIS_URL### is filled by t3lib_div::getIndpEnv('TYPO3_REQUEST_DIR').

Combining both will result in a faulty URL if you use - for example - just a slash as absRefPrefix.

Problem exists in all Extensions using ###THIS_URL### in Templates and its impossible to correct this issue by just changing the Template.

Solution is switching TYPO3_REQUEST_DIR to TYPO3_REQUEST_HOST - but this will break compatiblity to all extensions relying on that - such als direct_mail_subscription.

Another solution is adding a second value ###THIS_HOST### and fill it with TYPO3_REQUEST_HOST.

Optionaly: substituteMarkerArray or fillInMarkerArray could be extended to parse TYPO3-Enviroment-Variables by default. So if you use ###TYPO3_REQUEST_HOST### in a Template, it will be magicaly replaced by the value from t3lib_div::getIndpEnv('TYPO3_REQUEST_DIR').

(issue imported from #M14649)