Create XMP images

[openskies2009]

My objective is to create Metadata XMP files on the fly with images within directories and subdirectories, and add the description tag as "_null".
I dont really know where to start, i read the documentation but doesnt seem to indicate how to add a tag to the outputted XML file.

[Phil Harvey]

The command to do this is:

exiftool -srcfile %d%f.xmp -description="_null" -r DIR

- Phil