I lost the page where I entered my guesses, but I had a number of no's. I checked integers, decimals, negative values and constants like pi and e (didn't accept them, only accepts properly formatted numbers). It doesn't have infinite precision - for example, it will give this a no:
1.0000000000000000000000001 1.0000000000000000000000002 1.0000000000000000000000003
Given this, now what's the rule?
--Percy