Overlapping of images - Limiting system of dealing with multiple images?

     Every time I re-read information about multiple backgrounds in CSS3, I notice that it is repeatedly stated that multiple backgrounds are best overlapped.  But doesn't this seem like a really limiting way of doing multiple backgrounds?  What if I want to put images on the far left and far right sides of the container, plus one down the middle?  The current system either forces the use of pixels for sizing, or assumes that the designer will overlap images.  What if these images are PNG's with transparent sections, or SVG's?  Then overlapping breaks the images and there is no way of avoiding it.
     Instead of this really limiting system, I suggest allowing the user to use the rect() and inset-rect() structures as values in background-position, which could then be used as bounding boxes for the image behavior.  Images could then be tiled in the bounding boxes, without danger of overlapping destroying transparency effects.  They would also allow the users to position background images with respect to the right and bottom edges of the container, something which otherwise could only be done with calc().

Background-size & stretching

     I believe that background-stretch would be a better name for this property, if for no other reason than it's more telling of the property's true effect on background images.  Though IMPO, maybe it would be better for stretch/round to be specified through another property (with default value tile or repeat), and use background-size as a modifier to the images' intrinsic width/height.

More values for background-origin?

     I believe that background-origin should contain more values.  Other than padding and border, there should at least be a value 'root' which positions images with respect to the document (like background-attachment: fixed, except not fixed to the viewport).  In fact, maybe it would be better if background-attachment only determined whether elements scroll or are fixed, and let background-origin determine what they're fixed to (but this might break backwards compatibility).  I have found in CSS design there are situations which call for the ability for different containers to be able to position elements with respect to one common location, and at the moment the only way to do so is either using background-attachment: fixed (and attaching the image to the background may not alway be the desired result), or by manipulating the value of background-position (which isn't always an option).
     Also, maybe there should be a way to pick a parent element to be the origin of the image lineup.  Though this may be hard to do in a reasonable way and may not make much sense, since I believe root and background-position could do something like this.
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