A clever use for U+202E
There's been some discussion of the security implications of Unicode characters. In particular, some people worry that hackers could use Unicode characters to create strings that look just like other strings but behave very differently.
The Unicode U+006F ("o") looks a lot like the Unicode U+03BF ("ο"), for example, so that it's hard for people to tell the difference between "Google" and "Goοgle," even though they're actually different strings.
But there's a way to make Unicode even trickier, and that's by using the character U+202E, the "right to left override."
Here's the alphabet
and here's the alphabet with a single U+202E inserted in the middle of it
Note how the entire second half of the alphabet is displayed backwards when this single additional character is added. (If you can't see this, then your browser probably doesn't handle Unicode correctly. I tested it in IE 8 and Chrome 10 and it worked with both of them.)
And if you copy and paste the last three characters of the alphabet with the embedded U+202E, you'll find that when you select and copy the "PON" and paste it you get "NOP" back because the U+202E isn't in the part that you copied. You may think that you're selecting "PON," but you're really not.
Now imagine how a clever hacker could take advantage of this.