XML in HTML

In today's techniques phone call, the issue of what happens with MathML
inside browsers/user agents that don't support MathML.  MathML's <math> tag
allows for the attributes "altimg" and "alttext".  However, if the user
agent doesn't understand MathML (or more generally, any XHTML extension), it
is not likely to understand that it should use those attributes and so they
are irrelevent.

I did a quick look through the techniques document and did not see anything
about using non-HTML elements such as MathML, SVG, etc.  Both of these and
other non HTML extensions (eg, SMIL) are mentioned.  Is this an issue that
needs to be addressed?

Neil Soiffer                     email: neils@dessci.com
Senior Scientist                 phone: 562-433-0685
Design Science, Inc.             http://www.dessci.com
"How Science Communicates"
MathType, WebEQ, MathPlayer, Equation Editor, TeXaide