Overlapping sprites -- highest z level gets control and others are ignored

[Scott Ferguson]

This will work if all overlapping sprites (Ball or ImageSprite) have a different Z property value.

A sprite that is considered 'above' another sprite should have a higher Z property value than the one below it.

In this example, a red, green and blue circle overlap.

The blue circle has the highest z level.

When the blue circle is touched where all three circles overlap, it executes it's block to display 'You touched the Blue ball!'