What this says, in case it's not obvious, is that you can't get away with
<img src='madonna.jpg' src='child.jpg'>
One of the nice side-effects of this rule, for a programmer, is that all the XML processors and libraries have a function that, given an element and the name of an attribute, can return the value of the attribute, without having to worry about multiple occurrences. Of course, such a function can also signal that there was no such attribute on that element.
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