an Extensible Data Format, implmented in XML
Seems to be used a lot in astronomy, yay!
Here is the jargon
from the web site:
XDF is a common scientific data format based on general mathematical principles, object models, and XML that can be used throughout the
scientific disciplines. It includes these key features: hierarchical data structures, any dimensional arrays merged with coordinate information, high
dimensional tables merged with field information, variable resolution, easy wrapping of existing data, user specified coordinate systems,
searchable ASCII metadata, and extensibility to new features