Function is_escaped 

fn is_escaped(bytes: &[u8], start: usize, pos: usize) -> bool

Whether the byte at pos is escaped by an odd-length run of \ immediately before it (bounded below by start). Backslashes pair up (\\ is a hard break, not an escape), so only an odd count escapes the following byte. The label scanners use this so a \< opens literal < text instead of a label.