Version "2" of Xdmf can be found at:
git clone git://xdmf.org/Xdmf.git
There are two important branches in the repository, "master" and "pv". The "pv" branch was restructured during the ParaView 4 release to update it to be compatible with VTK 6.x's modularized build system.
The updates to Xdmf in version 2 are summarized in this paper: