Attention

TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.

tx_*

The tx_ prefix key is not used in the core itself, and is just a reserved space for extensions to never collide with core options, a use case could be tx_news for the news extension. Extension developers should create a key like that: tx_[extension key with no underscore]