> It ought to say "to execute the commands embedded in this data, Excel needs to start another application," so that people bloody well know that they're not just viewing data but they're actually doing something.

That's an astute observation.

Somewhat related:

Awhile back I remember seeing a demo of some Mozilla tech that would let one rotate a web page and then view a 3d "stack" of all the DOM elements. A bit like each layer was made up of different colors of lego blocks.

Is there some similar visualization tool to help distinguish data from code?

For example, imagine I want to use some scissors to clip some daisies on a hilltop. I eyeball the daisies I want. When I pick up the scissors they snap a picture of the daisies and cut 1000ft below until they split into the bedrock. Consequently, a demon's fiery arm shoots out the hole holding my scissors, violently cuts the daisies, then picks them up and offers them to me as a low, rumbling voice announces: "Daisies."

Now I don't know about anyone else, but I think that experience would make me a wee bit cautious about picking flowers. Or at least more than I would be merely by reading a man page.

Edit: I guess to be sensible, the demon's arm would need to recede back into the bedrock and heal the split.