Linux is a plus. Even documentation of the file format would do.
As someone who used to maintain an app that parses that XML file (sadly obsolete now) I can tell you that the big problem with that file isn't necessarily parsing it (although their choice of certain approaches in the XML makes baby Jesus cry) the big problem is that since the file format is almost XML, and 'internal' to WotC, they feel free to change it at will. Sometimes, changing it in small ways, sometimes in big ways. So the trouble for 3rd party Import/Export tools is not deciphering the insanity, its repeatedly deciphering the insanity.
Further, the actual "XML" (note the quotes) is filled with references to internal IDs in their database; so one can't properly create these files without either cracking their DB (you'll get in trouble) or using CB to generate the full permutation of valid options, and extracting their IDs into your own system, and then using your system to generate the XML. You can't save the intermediate step, though, or you'll get in trouble (Illegal copy of their IP). Plus, you wouldn't want to anyway; those IDs are far from static.
Most of it is pretty straight forward if you have a few examples to work from. It's missing quite a bit of information as others have pointed out. What you want to do with the file might help us get you going. For instance in i4e the import site can now create a new character without the .dnd4e file and you can then import it into the app as if you had started with one. I know the files pretty well at this point so if you run into something feel free to message me.
I found this enworld thread that states:
Well, the .dnd4e file is nothing but a text file with XML in it.
That means you could open it up (and you might have to change the extension to .xml) and you should be able to look at it.
One issue (described in the same thread) is that power descriptions and text are stored in a database inside of the character builder app itself and are not included in the .dnd4e file.