I'm writing my own blog/CMS engine (using WebApp and Google App Engine), and I'm looking for a light-weight XML format to use for content storage. Is there some already existing format that could be used for this purposes? Maybe some subset of the DocBook or ePub format? I had a look at those and they seem to be a little of overkill for what I want to do. Then again WXR (Wordpress eXtended RSS) or the one from Pluxml (pluxml.org) might be suited as well. Any ideas?