Check well-definedness and schema conformity of MathML markup

[physikerwelt]

No description provided.

[AndreG-P]

@physikerwelt
What's the idea here? Having a feature that does it optionally?

Currently, we have a notification system that prints warnings if something violates markup/schema. The user can change the notification system to exceptions rather than printing warnings. So we already have a system like that.

I have to verify that again, but I remember that nothing worked anymore if we stick too strictly to the schema/markup rules. It already starts with the first (doctype declaration) which already violates the definition rule.