The HF and the External scripting functionality works in the same way. I have one sample that I can show a little of (but not the whole thing as it was delivered as part of a professional services installation.
Here's the external component configuration:
When this node executes we concatenate the path to the script file and the parameters and make a CLI call.
Here's the parameters in their entirety:
"$FFin$" "C:\Xerox\FreeFlow\Core\Data\Save Destinations\Pad Barcodes\File - $FFOrder ID$.pdf" "C:\Xerox\FreeFlow\Core\Data\Save Destinations\Pad Barcodes\File - $FFOrder ID$ - merged.pdf" "$FFout$"
$FFin$ is the job file.
$FFOrder ID$ is the Manifest Order ID (this is to ensure the referenced files have a unique name)
$FFout$ is the folder into which $FFin$ should be saved after it is modified.
This this is a batch file, the parameters are referenced as %1, %2 and %3 within the script.
The Batch file invokes a CLI app to manipulate the file and then moves the file to $FFout$ (referenced as %3 within the batch file).
There's no scripting as such related to the MAX interface.
If you enable the scripting in the HF, it would typically be for converting other data into a manifest which we can then consume.