extending the composer with a new tag

[Fabrice Esti�venart]

Hi,

I'm a newbie in Mozilla Development and I need some tips to extend the 
composer with a XHTML non-conform tag called <meta:element>.
The main goal is to allow user insert that tag around the HTML tag 
selected in the structToolbar.

To achieve this, I need to add a <menuitem> in the <popup 
id="structToolbarContext"> and to associate it a treatment that consists 
 in adding a father element to the selected HTML tag.

What are the important files to look in ?
and how to easily manipulate the DOM object representing the loaded HTML 
document ?
Are there good references about that specific topic ?

aTdHvAaNnKcSe

Fabrice