From catalog/rfc9110-http.abnf rule: Via
Definition
Via = *( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
protocol-version = token
protocol-name = token
received-by = pseudonym [ ":" port ]
pseudonym = token
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
port = {File: rfc3986-uri.abnf Rule: port}
{File: rfc3986-uri.abnf Rule: port} = *DIGIT
comment = "(" *( ctext / quoted-pair / comment ) ")"
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
ctext = HTAB / SP / %x21-27 / %x2a-5b / %x5d-7e / obs-text
obs-text = %x80-ff
RWS = 1*( SP / HTAB )