Force CKEditor to use a class for images

Hi all,

Im looking to get CKEditor to use a class when placing an image rather than inline styles, a bit like the editor on WordPress.

I could then define how the image is to be inserted, margins, borders etc.

I can see that you can use dataProcessor.writer.setRules when instantiating the editor but I cant find a list of the possible rules or anywhere that mentions how to do it for classes.

Any help greatly appreciated.

Thanks
Rolf