( "Referred‑By" /  "b" )  HCOLON  referrer‑uri  *( SEMI  ( referredby‑id‑param /  generic‑param ) )

; example:
; Referred-By: <sip:referrer@referrer.example>
;   ;cid="abnf-20398823.2UWQFN309shb3@referrer.example"

( name‑addr /  addr‑spec )

"cid"  EQUAL  sip‑clean‑msg‑id

LDQUOT  dot‑atom  "@"  ( dot‑atom /  host )  RDQUOT

atom  *( "."  atom )

1*( alphanum /  "-" /  "!" /  "%" /  "*" /  "_" /  "+" /  "'" /  "`" /  "~" )