The latest spec can be found here:
http://www.loc.gov/standards/datetime/ISO_DIS%208601-2.pdf
Here are some differences I've noticed between the current implementation and the latest spec. (this list may not be complete):
- use of
% to mean both uncertain and approximate (see 4.2 Uncertain and/or approximate date)
- use of capital
X instead of lowercase u for unspecified digits (see 4.3 Unspecified)
- use of a blank instead of the keyword
unknown (see 4.4 Enhanced time interval)
- use of
.. instead of the keyword open (see 4.4 Enhanced time interval)
- use of a capital
Y instead of a lowercase y (see 4.5 Year exceeding four digits)
- use of uppercase
S instead of lowercase p to express significance (see 4.6 Significant digits)
- there's also a whole section on recurring dates that may or may not be applicable (see 5 Repeat rules for recurring time intervals)