The element <purpose> describes the purpose of the dive; this element was adopted from the DL7 Standard by DAN — Project Dive Exploration, http://www.diversalertnetwork.org/research/projects/pde/.
Allowed keywords are: sightseeing, learning (if the owner of the UDDF file is a student diving with an instructor on an educational dive), teaching (if the owner of the UDDF file is an instructor teaching a student), research, photography-videography, spearfishing (unfortunately, even nowadays not frowned upon :-( ), proficiency, work, other.