Statics Fields Relevant to ImageBvr Objects

detectableEmptyImage: An image behavior (ImageBvr object) in which all points are transparent but detectable. This image is useful for blocking mouse input from an underlying image, allowing that input to be redirected. The bounding box is of infinite extent.
emptyImage: An image behavior (ImageBvr object) in which all points are transparent and undetectable. This has an empty bounding box, which means that its maximum point is less than its minimum point. This allows operations such as union and intersection to produce the correct results.