CSS3 draft: multiple backgrounds concerns

I have done some experimenting with multiple backgrounds using Safari  
and have read the CSS 3 draft specifications 3 or so times with  
regards to borders and backgrounds, and I think there needs to be  
some improvement on the positioning of repeated backgrounds.

I think one of the most common uses of the new multiple backgrounds  
is going to be rounded-rectangles or similar fancy rectangles, that  
being different images for the corners and repeated segments on the  
edges.

 From my experimentation, I was able to reproduce a rounded rectangle  
using a single style, however the background of the corners needed to  
be opaque so that the repeating edges did not show through.

Unless I have a misunderstanding of the standards or didn’t read them  
clearly enough or there is a problem in the rendering from Safari, I  
believe there should be an method for specifying where a ‘repeat-x’  
background should begin relative to the left of the box and end  
relative to the right of the box. There should also be similar method  
for ‘repeat-y’ and ‘repeat repeat’ backgrounds.

A possible solution may be changing the background-repeat property  
values to include boundaries, a possible example may be:

..someStyle{
             background-image: url(someBackground.png);
             background-repeat: repeat-x 10px 15px;
}

-Charlie Hayes