TYPO3 Core

Validating a field via a TCA setting of:

'is_in' => 'a b'

will result in a check for "a", "b" or "blank/space" in FormEngineValidation.js

while

'is_in' => 'ab '

will result in a check for "a" and "b" only (the setting from the TCA gets trimmed and is missing the space in FormEngineValidation.js)

Most probably this was included to prevent unintended allowance of blanks/spaces. When explicitely aiming for allowing spaces/blanks this seems counter-intuitive though.

Suggestions:
Either to not trim the value given in 'is_in' or add a short comment to the according documentation in https://docs.typo3.org/typo3cms/TCAReference/ColumnsConfig/Type/Input.html#columns-input-properties-is-in