I've been trying to validate the current MathML schema and I'm getting the unhelpful error message "E Null" as a result. I've figured out that that means that a schemaLocation is missing (but agreed with others that this should be expanded into something that doesn't take so much research to figure out). Anyway, the line that is causing me trouble is: <xs:import/> This line is followed by the helpful comment "import any foreign namespace". Now I know that "This simply allows unqualified reference to foreign components with no target namespace without giving any hints as to where to find them." but the schema doesn't contain any such references as far as I can see and commenting out the line allows it to validate. Perhaps it would be more useful to get Oxygen to defer its disapproval until it finds a reference for which no definition exists? Or am I misunderstanding what is going on here. Steve