Function parse_u_plus 

fn parse_u_plus(mencode: &str) -> Option<char>

Parse a U+XXXX style mencode — 1 to 6 hex digits after the literal U+ prefix — and validate the result via char::from_u32. Returns None for surrogates, non-characters, and out-of-range integers, rather than panicking, so malformed input falls cleanly through to the description fallback.