A WorldWindow is a SystemWindow whose central area presents an inner Morphic world.

WorldWindows have a red title bar when the world inside is inactive. This changes to green when the world becomes the active world. The world inside becomes activated by clicking in it. When you click outside this world, the parent world resumes control. While its world is inactive, the WorldWindow may be moved and resized like any other.

It would be nice to make the world inside active whenever the WorldWindow was active, but this presents difficulties in moving and resizing, probably related to use of the global World instead of self world in many methods.

This facility is mainly the work of Bob Arning, with a number of tweaks by DI.

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	buildWindowMenu
	collapseOrExpand Collapse or expand the window, depending on existing state
	extent: Set the receiver's extent to value provided. Respect my minimumExtent.
	fullBounds Return the bounding box of the receiver and all its children. Recompute the layout if necessary.
	mouseUp: Handle a mouse up event. The default response is to let my eventHandler, if any, handle it.
	openInWorld: This msg and its callees result in the window being activeOnlyOnTop

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	test1 WorldWindow test1.
	test2 WorldWindow test2.