It’s just data

HOWTO Embed MathML and SVG into HTML4

This is a proof of concept.  I’ve gotten it to work on Firefox, and believe similar techniques would work on Opera and nightlies of WebKit.  It does not add MathML or SVG support to browsers that don’t already have it, it merely enables browsers which already recognize these grammars in XHTML5 to render similar structures when found in HTML4 documents.