This by itself is a great selling point of d3, in my opinion. You can inspect everything about your visualization using the browser debugger, and it's easy to

This by itself is a great selling point of d3, in my opinion. You can inspect everything about your visualization using the browser debugger, and it's easy to figure out how the objects in the DOM correspond to your code, which is a blessing. The first thing anyone should do when checking out d3 is go through a simple example and then open up the debugger and see how transparent the connection is. Also, I think a non-programming designer could understand and tweak the CSS without much guidance from a developer, using only an understanding of SVG.