WIDGET_API void       XPGetElementDefaultDimensions(
                         XPElementStyle       inStyle,    
                         int *                outWidth,    /* Can be NULL */
                         int *                outHeight,    /* Can be NULL */
                         int *                outCanBeLit);    /* Can be NULL */

This routine returns the recommended or minimum dimensions of a given UI element. outCanBeLit tells whether the element has both a lit and unlit state. Pass NULL to not receive any of these parameters.