Corner Case, Edge Case

I got a message in my mailbox the other day entitled 'highschool fun', and it's only by some small miracle I didn't delete it before noticing it actually came from one of my former high school classmates. Isn't that sad, somehow?

One of the nice things about Apple's OS X mail client is that you can configure it to not download images, so that the ten daily 'high school barnyard fun' emails that arrive in glorious full HTML won't actually render in the preview panel just as your boss walks into the office. And now we have Apple's OS 10.2 client, which ( rumor has it ) uses latent semantic analysis to auto-identify spam. I feel a completely misplaced sense of pride.

It was another beautiful clear day, and I spent a significant part of it trudging up a mountain with the better half, looking for Abby pond, which the beavers built. We forded rivers, swamps, and streams, but no pond did we find, only rocks that hurt the feet, and the occasional highly suspicious chipmunk. Still, the leaves were magnificent, and just a few hundred yards up the first hill there grew a single thistle, with a pretty pink bloom, right by the side of the path. He was the only thistle in the whole forest, as best I could tell, and I think it was a good omen.

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Computer friends of the Internet -- I am trying to find out what the difference is between a corner case and an edge case ( debugging terminology ), and if anyone can tell me, I will send them a Mallomar.