caret

I would expect the same output of the following two commands, but the first one looks wrong to me: % echo abc^ABC.123 | sed 's/[^A-z0-9]/_/g' abc^ABC_123 % echo abc^ABC.123 | sed 's/[^[:alnum:]]/_/g' abc_ABC_123By the way, gsed does the same. Am I missing something?..