On validating with multuiple namespaces

What's about validating XHTML with embedded SVG or MathML?

Can existing schemas (XSD, Relax NG, etc.) describe documents which allow embedding of (arbitrary) other namespaces? (I'm not an expert in validation.)

That is I want a validator to ignore all elements of alien namespaces, or something like this.

I afterward may develop an application which will call validators multiple times, for every namespace in the document.

-- 
Victor Porton - http://portonvictor.org