HTML attr inline styles style rules
<image border="0"
    src="...">
<img style="border: 0px none"
     src="...">
#myImage {
   border: 0px none;
}

<img id="myImage" src=...">

The successor to Nvu will let you create style rules instead of HTML attributes or inline styles when you create an element. It already works beautifully here. I'm still struggling to find a nice and simple UI metaphor though.