Test that the viewer can handle the xlink:href attribute on patterns.
There are two rectangles with a pattern fill made up of 4 rectangles. The pattern definition of the lower one references the pattern definition of the upper one, using the xlink:href attribute. Because the particular way that the patterns and rectangles are defined in this test case, the two fills will appear the same - the rectangles are positioned on pattern-size boundaries, so that the offsets into the pattern at the left edges of the respective rectangles is identical.
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The test passes if the rendering matches the reference image, except for any differences in text due to CSS2 rules. Note that the top rectangle must look identical to the bottom rectangle.