This script can read from files, however it does not support reading child files for a given folder item in a Lister.
The script will calculate the column value for each item in the Lister. When read data from files in the Lister, the script will only ready each file once, even if there are many columns to calculate. Even so for large folders it can still be a bit slow.
Adding support for scraping child folders looking for files with a given value would complicate the file content caching logic quite a bit. It could be done but I'm not sure if this is the right script for it.
This remands me of another script that did something similar for descrypt.ion files.