Tests that reading of IDs and modification of id and xml:id is conformant to the SVG and xml:id specifications. The test passes if four green circles are shown.
The first circle has an id only; the second, xml:id only. The third circle has both, with the same values; and the fourth has both, with different values. All four circles have a red fill; on loading the document, a script
gets each of the circles by its ID and then sets the fill to green. Lastly, the script attempts
to get the fourth circle by ID, using the value of the id attribute; this must fail. If the fourth
circle is dark red, the implementation is not giving priority to the value of xml:id.
