[TYPO3-dev] Best practice to implement BE-preprocessing in a FE plugin

[Taras Sajuk]

Hi all,

Im working on a FE (content) Plugin.  The user should be able to enter
data in the plugin form, a File handle to be more specific, and this
data should be processed immediately in the BE - storing some excerpt
of the file in the extensions table.

However, I only see the possibility to store some validated data or to
call own processing _before_ user input in BE, to fill some selection
list.

Is there a best practice to call extension processing on user input in BE?
 --
Taras Sajuk