Test animation of external references.
This test uses three external SVG files, each with their own animation. The href attribute of an image element is animated to show the three images.
The animated image appears within the rectangle. The number of the image currently being shown is at the top right of the rectangle (embedded within the image itself).
The first image should extend the width of the three colored rectangles (matching the guides below the embedded rectangle).
The second image should extend the width of the bottom two rectangles from the value they obtained after the first image. The top rectangle does not change.
The third image should extend the width of the bottom rectangle from the value it obtained after the second image. The top two rectangle do not change.