>> Obviously for a SVG document with the full profile one can as well
>> reference a view element with id='xywh' with a viewBox(40,0,20,20)
>> to be able to note this:
>> background-image: image('sprites.svg#xywh')
>Unfortunately, it doesn't work in that way in <img> tags or
>background-image:url() attribute in current implementations.
Well, implementations have lots of bugs and gaps, not just for CSS or SVG.
There are much more of those bugs and gaps in implementations than
bugs and gaps in recommendations ;o)
This is only an indication, that implementations need to be improved
On the other hand - typically the 'bug probability' of documents
of authors is heigher than for implementations displaying such a document,
an indication as well, that the majority of content needs to be improved
It does not necessarily improve the situation, to specify yet another method,
incompatible and less advanced than that, what is already recommended.
>Also it isn't clear, will the image be clipped by the corresponding
>viewport, for example if it is centered. I assume it shouldn't and that
>differs from “Image Fragments”.
Fortunately in SVG the author can decide what is intended.
Unfortunately the clip property is corrupted in CSS 2.1. SVG 1.1 still follows
CSS2.0, but if viewers have a bug following CSS2.1, obviously they will fail
with clip, therefore better to use clipPath, clip-path etc.