For the time being we do not plan to provide such a feature, because it can be achieved with a little bit of CSS and an image. The idea I can give you is the following:
1. Use IE DevToolbar or FireBug to inspect the parent element of the content are <iframe />. You will notice that it is a <td /> with a .reContentCell CSS class name.
2. Create a large ruler
image with ticks and measurement units (for example 2000 x 2000 pixels, the idea is that it should be larger than your largest RadEditor) with a vertical and horizontal ruler. It should look like a vertically flipped "L".
3. Add padding-top to .reContentCell equal to the height of the horizontal ruler (the ruler itself, not the height of the entire image). Let's assume that it is 20 pixels high.
4. Add padding-left to .reContentCell equal to the width of the horizontal ruler (the ruler itself, not the width of the entire image). Let's assume that it is 20 pixels wide.
5. In your stylesheet use a CSS selector like this one:
padding: 20px 0 0 20px !important;
background: url('Ruler.gif') no-repeat !important;
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