The current DFDL spec dates from Sept 2014. There have been numerous corrections and clarifications listed in a separate errata document.
To assist the DFDL user and implementer community a preliminary version of this revised spec is being made available which has all errata integrated into it.
This is far easier to use and has change-tracking so the changes from the Sept 2014 revision are highlighted.
You'll find a link to this preliminary version here:
Keep in mind this is a work-in-progress and will change. This homepage
link will remain live, but the specific document link you find there
will break when new revisions come out.
This is hosted at the new OGF github site, and served using github pages.