Support for more Unicode characters. (supports future Unicode versions)
Character normalization (ie. an e followed by a combining accent acute can now be represented as é)
Some Unicode characters are now allowed but need to be escaped.
Namespace names are now defined as IRIs (Internationalized Resource Identifiers).
Prefixed namespaces can be undeclared (xmlns:pre="").
Problems: not backwards compatible, schema languages have not been updated to support these features.