The corners rounding natively works only on boxes, but the scripting extensions provide that feature also for frames and images.

Have in mind the following:

•A box with rounded corners "knows" about the rounding radius, and you can edit such rounding in the Rule Extra palette.

•A frame or an image with rounded corners "does not know" about the rounding, so the only way to edit such rounding is to remove it completely, and then apply a different one.

•The boxes with rounded corners cannot be neither selected, nor resized or reshaped by polygon tool .