Vector form content have the advantage that they store items in layers. Consider png format with bmp. In the former we can save and remove layers where as the latter is scalar content per pixel. If this layering approach were available to most web pages and views, then we could have a css that can define style to each layer.
For example, let us say we want to build a web page for a clothing and accessories store. The web page has to let users choose the clothing and dress up a mannequin. where different clothing can go one on top of each other. This we can do today with overlaying of images in .png format.
HTML:
<img id="img1" src="img1.png"/>
<img id="img2" src="img2.png"/>
<img id="img3" src="img3.png"/>
and we define the css for these as follows:
img
{
    position:absolute;
    top: 0px;
    left: 0px;
}
Now to cause the images to overlay, we set the z-index in css as follows:
#img1
{
z-index: 10;
}
#img2
{
z-index: 20;
}
#img3
{
z-index: 30;
}
This will overlay 3 on top of 2 on top of 1. Here 3 could be the accessory, 2 could be the mannequin and 1 could be the background.
To change the accessory, we could do :
<img src="accessory1.png" onClick="setAccessory('accessory1.png');"/>
and use javascript like so:
function setAccessory(path){
     document.getElementById('layer1').src = path;
}
To add more accessories, we can just define more layers.
Adobe's macromedia dreamweaver has the notion of dynamic layers. Any object can be added to the webpage by directly adding it to a layer. Then the layer can be moved around.