A big plus for xml are the options to validate (opinions in parenthesis):
- Schematron (extremely powerful)
- W3C XML Schema (solid)
- DTD (not so nice (it isn't even xml))
- XSD (most used)
And options to query data:
- XPath (in version 2.x even better)
- XQuery (mostly not of interest anymore)
YAML is probably the easiest to read for humans in most cases.
JSON is quite easy to read and it is the way JavaScript stores data (correct me if wrong).
I really like to use JSON when writing my own C style programming languages to parse values.
