The point about MathML is that it, being XML-based, can be readily checked for correctness against a DTD or schema - something .ENEX import already does. I would hope that'd be a big help in this. And, yes, I know the format alone isn't enough: As has been stated, authoring tools are required. One other thing: I would expect most browsers by now to be able to render MathML. Maybe that's naive. :-) Martin