Experiment with CEI.dtd

Hello, I tried to use CEI DTD available on CEI website, but I didn't success to use it. I think there is a problem in DTD file. I use XML oxygen, this software shows available elements in a node and <text> and <charter> elements aren't available in <CEI> root element. Evidently, if I use this element, I can't validate my XML file. So I can't use it and study the hierarchical structure (or i don't understand). Georg, can you explain the structure you thought ? Or can you classify different elements you propose in tag library ? Thank you. Best wishes Gautier