How about letting someone drag a piece around the board to see how it can move from different locations?
This does not seem like a good solution to me. They would need to know to do that (most pieces in most games don't move in different ways from different spaces) and dragging the piece around willy-nilly to see what happens doesn't seem very efficient. A note saying "the King cannot cross the river" would be the efficient way to communicate this. It isn't really possible for move diagrams to show the nuances of special rules. In Elk Chess, for example, the Elk moves like a Rook on light squares and a Knight on dark squares. Expecting the user to drag the piece around until he notices the pattern would not be reasonable. The diagrams give a quick overview of how the peices move, but to understand all the details, you still need to read the rules.
This does not seem like a good solution to me. They would need to know to do that (most pieces in most games don't move in different ways from different spaces) and dragging the piece around willy-nilly to see what happens doesn't seem very efficient. A note saying "the King cannot cross the river" would be the efficient way to communicate this. It isn't really possible for move diagrams to show the nuances of special rules. In Elk Chess, for example, the Elk moves like a Rook on light squares and a Knight on dark squares. Expecting the user to drag the piece around until he notices the pattern would not be reasonable. The diagrams give a quick overview of how the peices move, but to understand all the details, you still need to read the rules.