TYPO3 Core

You can encapsulate a finisher option value with {}.
This enables you to access every getable property from the TYPO3\CMS\Form\Domain\Runtime.
For example you can set the "subject" option value from the EmailToSender finisher to something like {textfield-1}.
If you do so, the subject option value will be filled with the submitted data from the formelement with the identifier 'textfield-1'.
This is done by the function TYPO3\CMS\Form\Domain\Finishers\AbstractFinisher::parseOption().
parseOption fails if such a referenced formelement value contains non text value like a DateTime object.
This happens if a formelement do some property mapping stuff.
With this patchset, parseOption replace finisher option values with formelement values only if the formelement value is a string.
In addition, this enables you to replace non text values with your custom finisher implementations.