Abstract : We introduce a method for building a minimal XML type (belonging to standard class of regular tree grammars) as an extension of other given types. Not only do we propose an easy-to-handle XML type evolution method, but we prove that this method computes the smallest extension of a given tree grammar, respecting pre-established constraints. We also adapt our technique to an interactive context, where an advised user is guided to build a new XML type from existing ones. A basic prototype of our tool is implemented.