It's an alternative to overlapping windows, a fundamental of the desktop metaphor.<p>I seem to recall seeing a demo of something similar, that was also from PARC (or maybe just in the same era, i.e. the 60's). Of course, the desktop metaphor won, and work didn't continue on the other. I mention it not to preempt you, but because seeing that work would give you an extra perspective, and a bunch of experiments for free to see what works/doesn't work.<p>Or maybe it was an infinite desktop, where you could zoom in/out to find things. Would that count as "fluid"? Sorry, think I'm rambling.