pub fn reliable_sequence(response: &Response) -> Option<u32>Expand description
Whether a provisional response was sent reliably, and its sequence number.
§4: a 100 Trying is hop-by-hop, so a Require: 100rel on one “MUST be ignored”. Checking
the status here rather than at the call site is what stops a proxy’s 100 from being
PRACKed at a UAS that never numbered it.