I've never come across this one, thanks for the tip. I like the way it doesn't use every character in the range 0x20 to 0x7f. That last one in particular (0x7f or 'DEL') has always seemed problematic to me because it's a weird exceptional case. I've always thought someone must have screwed up with that one way back in the day. Using only '!' to 'u' and hence avoiding ' ' feels right for some reason, and I also like the cute trick of getting just a little bit of compression by using 'z' to represent 32 zero bits.