Constant CONNECTION_SPECIFIC_HEADERS 

pub const CONNECTION_SPECIFIC_HEADERS: [&'static HeaderName; 5];

Available on crate features http and std only.

Connection-specific fields prohibited in both HTTP/2 and HTTP/3.

See RFC 9113 Section 8.2.2 and RFC 9114 Section 4.2. TE is checked separately because requests may contain TE: trailers. Trailer is not prohibited; it can announce trailing fields in these protocols.