Function split_attributes 

pub fn split_attributes(raw: &str) -> Vec<(usize, &str)>

raw cut into attributes at every attribute_starts offset that whitespace precedes, each with its byte offset in raw and trimmed. An @ with no whitespace before it (@deny(x)@allow(y)) does not cut, so the run-together text reaches the validators whole and is refused there with a message naming both halves.