[abnf-discuss] ABNF colloquialism for end-of-line

[Sean Leonard <[e-mail]>]

Hello ABNF “Doctors”:

On a recent thread on cbor@ <https://mailarchive.ietf.org/arch/msg/cbor/ZL2NvalH6jmSVqfvkBH4af3BHsE>, the following question arose:
What is the best ABNF colloquialism for end-of-line?

CR LF is the “Internet standard newline”, with rule name <CRLF> [RFC5234]. However, there is a desire amongst some specification writers to admit Unix LF as well. I have not heard of people clamoring for bare CR; however if bare LF is on the table then bare CR might be on the table too, for completeness. A quite small minority of published RFC specifications define an end-of-line production as CRLF / LF, and an even smaller minority of published RFC specifications allow for bare CR as well.

So I just wanted to see what ABNF people’s opinions are on this one.

Thanks,

Sean

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2017-11-15 Facts about CRLF and new lines in ABNF in RFC Series
Sean Leonard

Facts about CRLF and new lines:

Surveyed ABNF of all RFCs between RFC 2000 to RFC 7999.

“What is the end-of-line marker called, other than CRLF?” (by search of CRLF)

Answer: Most call it CRLF. Amongst the minority, EOL is the most common, followed by line-break or lineBreak. Most define the end-of-line marker as CR LF; in the minority, most in the minority use CRLF / LF, and a smaller subset uses CR / LF (aka any of bare CR, bare LF, or CRLF).

RFC	Hint	Name	=	Definition
2705	Megaco	EOL	=	CRLF / LF
2967*	TISDAG	nl	=	%d13 %d10
2967*	TISDAG	SEP	=	(CR LF) | LF   <-- NOT actually ABNF 
3108	SDP	EOL	=	(CR / LF / CRLF)
3435	Megaco	EOL	=	CRLF / LF
3780	SMIng	lineBreak =	CRLF / LF
4997	ROHC-FN	CRLF	=	%x0A / %x0D.0A
4997	ROHC-FN	NL	=	COMMENT / CRLF
4997	ROHC-FN	COMMENT	=	"//" *(SP / HTAB / VCHAR) CRLF
5228*	Sieve	(Sieve explicitly limits to CRLF-only in text)
5234*	ABNF	c-nl	=	comment / CRLF
5234*	ABNF	comment =	";" *(WSP / VCHAR) CRLF
6020	YANG	line-break =	CRLF / LF
7208*	SPF	CRLF	=	<standard end-of-line token as per [RFC5322]>
7468	PKIXt	eol	=	CRLF / CR / LF
7468	PKIXt	eolWSP	=	WSP / CR / LF
7468	PKIXt	W	=	WSP / CR / LF / %x0B / %x0C


“How is ‘nl’ defined?” (by search of ‘nl’)

Answer: Always CRLF.

RFC	Hint	Name	=	Definition
2957	whoispp	nl	=	%d13 %d10
2958	whoispp	nl	=	%d13 %d10
2967*	TISDAG	nl	=	%d13 %d10
4997	ROHC-FN	NL	=	COMMENT / CRLF
5234*	ABNF	c-nl	=	comment / CRLF
5234*	ABNF	comment =	";" *(WSP / VCHAR) CRLF
6787*	MRCPv2	phrase-nl =	"Phrase-NL" ":" 1*UTFCHAR CRLF


“How is ’newline’ used?” (by search of ‘newline’) 

Answer: ‘newline’ is never defined as a rule name. When it appears in comments, it is *always* associated with CR LF only. (Same as ‘nl’.)

“How is ‘0A’ used?” (by search of 0A)

Answer: ‘0A’ is almost always defined as LF or used as LF; no additional interesting variations were uncovered. The only interesting variation is RFC 4464, which has %x0a / %x0d / (others) as whitespace generically, but that protocol is not line-oriented.

* items do not address the premise of the inquiry, but is included anyway for completeness.
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