MathML generator

I assume this is some sort of an academic project.
I'am sorry but to me it just looks like a html form, with a text area and some javascript, to append fixed text strings to the text area.

It doesn't really help me write expressions like

<mrow>
<mo> + </mo>
<mi> a </mi>
<mi> b </mi>
</mrow>

I don't speak french, so perhaps I'am misunderstanding something, but to me it seems like your 'valider' function doesn't do anything, and your 'Aperu' function displays the MathML expression without any kind of styling. All in all I'am not impressed (admittedly I'am not easy to impress).

If you are really serius about making an MathML editor, I might suggest that you take a look at http://www.bitfluxeditor.org/ . By writing an XML schema for MathML with some custom code for Bitflux, and some XSL stylesheets you should be able to create a very impressive MathML editor (this might be quite a lot of work for you).