I already found these two threads diskussing writing of XMP data in XnView:
http://newsgroup.xnview.com/viewtopic.p ... 63&start=0
http://newsgroup.xnview.com/viewtopic.p ... 63&start=0
Especially the sentence "Currently xnview can't write XMP, but will be added..." sounds interesting.
Unfortunately it's from September 2007

So what's the current status on this?
Maybe I should describe, my use case for this feature:
I have all my photos on my PC (the "original" files) and keep a backup of the directory structure on a NAS using robocopy.
With XnView I have a very comfortable tool to view and rate those photos. Unfortunately the rating is only written to the DB and not to the image files.
This means that I don't see the rating when looking at the backup images on the NAS.
Also other applications cannot access XnView's DB, but some of them are able to read XMP informations.
It would be a real improvement, if I could chose to use XMP fields instead of the DB for saving the rating.
Of course, the same would be useful for colour labels as well, but I'm not using those.
Saving the tags inside the image file would also be appreciated, but I'm not shure if there is a standardized XMP field for this.
Can we hope to see a version that writes and reads XMP data to/from image files in the near future?
Thanks for all comments on this!