TYPO3 Core

File: EXT:rte-ckeditor/Configuration/RTE/Processing.yaml

Line removeTags: [center, font, link, meta, o:p, sdfield, strike, style, title, u]

This does not work at all. Parser does ignore this line and removes none of these tags. These configs are transported to TSconfig as-is. TSconfig expects a CSV (and no array) there!

Correct is: removeTags: center, font, link, meta, o:p, sdfield, strike, style, title, u - then the parser removes the tags.

Discovered in v12, but I assume this never worked since the introduction of CKEditor.

I discovered this because CKEditor 5 does not allow getting rid of p-tags in RTE anymore (contrary to CKEditor 4, which had enterMode and autoParagraph settings). So at least the core persisting to DB should get rid of the p-tag once I add "p" to removeTags. It did not work and it did also not work for any other tag. So I switched from Array to CSV, and it instantly worked.

I did not test other config options, but I can imagine that other configs are also using arrays where TSconfig expects CSV.

Be careful: If you fix this then ALL setups using the shipped default RTE Presets after the update will then suddenly respect this setting and remove tags upon saving. Maybe there are people that just use the default config but still want to keep tags and are just not aware that some tags actually are forbidden by default.