the [^ part negates the characters inside the []. So it'll match anything that is NOT 0-9a-z, case insensitive /i. The !~ then says that str should not match

the [^ part negates the characters inside the []. So it'll match anything that is NOT 0-9a-z, case insensitive /i. The !~ then says that str should not match the regex. so you end up with it saying that str should not match anything other than 0-9a-z case insensitive.