ABNF

• 参考
  wiki
  RFC内のルール

• 抜粋

token          = 1*tchar

tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                    / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
                    / DIGIT / ALPHA
                    ; any VCHAR, except delimiters
OWS = *( SP / HTAB )

RWS = 1*( SP / HTAB )