The ABNF you propose has the problem that it forces the tag param to be the first param. RFC 3261 forbids the tag parameter to appear more than once by the following text at the top of page 32 in section 7.3.1:
Even though an arbitrary number of parameter pairs may be attached to a header field value, any given parameter-name MUST NOT appear more than once. Hope that helps. AlexC -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Srivastava, Samir Sent: October 29, 2003 8:54 PM To: [EMAIL PROTECTED] Subject: [Sip-implementors] ABNF tag-param in FROM/TO Hi, Below is ABNF from 3261 for tag-param. >From = ( "From" / "f" ) HCOLON from-spec from-spec = ( name-addr / addr-spec ) *( SEMI from-param ) from-param = tag-param / generic-param tag-param = "tag" EQUAL token To = ( "To" / "t" ) HCOLON ( name-addr / addr-spec ) *( SEMI to-param ) to-param = tag-param / generic-param It allows multiple tag-params in to and from headers. As "*" is put for allowing any number of repetitions of {from|to}-param, which can have multiple tag-param itself. We should limit it, at the most one occurrence of it, using Section 3.6 of RFC 2234 . I would suggest something of following syntax :- To = ( "To" / "t" ) HCOLON ( name-addr / addr-spec ) to-additional-param to-additional-param = ( 0*1(SEMI tag-param)) / ( *(SEMI generic-param)) The same applies to ABNF in Replaces and Join Header drafts for replaces-param and join-param. Thx Samir _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
