Re: Implementation of semantics

> 1) Does the following implementation make sense for a browser without Content MathML support:
> 
> - Test if the first child is a presentation MathML element and if so, display it.
> - Otherwise, read the list of other children in that order and display the first <annotation-xml> with a known encoding ; or a plain text <annotation> if one is found.


That makes sense to me.

> 3) What are the official encoding values other than MIME content-type? The REC mentions "Content-MathML", "Presentation-MathML" for backward compatibility. The W3C note http://www.w3.org/Math/Documents/Notes/graphics.xml#svg-in-mathml-guidelines also contains the "SVG1.1" value, but is it official?

I do not think this is official but making it present on a public document for a long time makes it inevitably used. So if there's an option to accept it when implementing, I'd go for that, especially since it's not ambiguous. 
TeX had far too many media-types, for example, spread around the world... (and none specified that I know of).

Paul