I was suggested during last Libre Graphics Meeting edition, that Open Raster should use XMP for it metadata (XMP is the metadata specification that rules them all, exif, iptc... your own metatada specification as well). But until very recently, both the specification and the library were available under a very dubious license which was incompatible with GPL (and with a Open Formats). But Adobe did hear to our complaint, and decided to release under BSD. So, now nothing prevent a wider use in the Open Source world, and that's really cool.

So thanks to Adobe, and if you want to play with XMP go download it from here.