Diff: rfc2234.txt - rfc4234.txt

	rfc2234.txt	rfc4234.txt


	Network Working Group D. Crocker, Ed.	Network Working Group D. Crocker, Ed.
	Request for Comments: 2234 Internet Mail Consortium	Request for Comments: 4234 Brandenburg InternetWorking
	Category: Standards Track P. Overell	Obsoletes: 2234 P. Overell
	Demon Internet Ltd.	Category: Standards Track THUS plc.
	November 1997	October 2005

	Augmented BNF for Syntax Specifications: ABNF	Augmented BNF for Syntax Specifications: ABNF


	Status of this Memo	Status of This Memo

	This document specifies an Internet standards track protocol for the	This document specifies an Internet standards track protocol for the
	Internet community, and requests discussion and suggestions for	Internet community, and requests discussion and suggestions for
	improvements. Please refer to the current edition of the "Internet	improvements. Please refer to the current edition of the "Internet
	Official Protocol Standards" (STD 1) for the standardization state	Official Protocol Standards" (STD 1) for the standardization state
	and status of this protocol. Distribution of this memo is unlimited.	and status of this protocol. Distribution of this memo is unlimited.

	Copyright Notice	Copyright Notice


	Copyright (C) The Internet Society (1997). All Rights Reserved.	Copyright (C) The Internet Society (2005).


	TABLE OF CONTENTS	Abstract


	1. INTRODUCTION .................................................. 2	Internet technical specifications often need to define a formal
		syntax. Over the years, a modified version of Backus-Naur Form
	2. RULE DEFINITION ............................................... 2	(BNF), called Augmented BNF (ABNF), has been popular among many
	2.1 RULE NAMING .................................................. 2	Internet specifications. The current specification documents ABNF.
	2.2 RULE FORM .................................................... 3	It balances compactness and simplicity, with reasonable
	2.3 TERMINAL VALUES .............................................. 3	representational power. The differences between standard BNF and
	2.4 EXTERNAL ENCODINGS ........................................... 5	ABNF involve naming rules, repetition, alternatives, order-
		independence, and value ranges. This specification also supplies
	3. OPERATORS ..................................................... 5	additional rule definitions and encoding for a core lexical analyzer
	3.1 CONCATENATION RULE1 RULE2 ............................. 5	of the type common to several Internet specifications.
	3.2 ALTERNATIVES RULE1 / RULE2 ................................... 6
	3.3 INCREMENTAL ALTERNATIVES RULE1 =/ RULE2 .................... 6	Table of Contents
	3.4 VALUE RANGE ALTERNATIVES %C##-## ........................... 7
	3.5 SEQUENCE GROUP (RULE1 RULE2) ................................. 7	1. INTRODUCTION ....................................................2
	3.6 VARIABLE REPETITION *RULE .................................... 8	2. RULE DEFINITION .................................................3
	3.7 SPECIFIC REPETITION NRULE .................................... 8	2.1. Rule Naming ................................................3
	3.8 OPTIONAL SEQUENCE [RULE] ..................................... 8	2.2. Rule Form ..................................................3
	3.9 ; COMMENT .................................................... 8	2.3. Terminal Values ............................................4
	3.10 OPERATOR PRECEDENCE ......................................... 9	2.4. External Encodings .........................................5
		3. OPERATORS .......................................................6
	4. ABNF DEFINITION OF ABNF ....................................... 9	3.1. Concatenation: Rule1 Rule2 ................................6
		3.2. Alternatives: Rule1 / Rule2 ...............................6
	5. SECURITY CONSIDERATIONS ....................................... 10	3.3. Incremental Alternatives: Rule1 =/ Rule2 ...................7
	6. APPENDIX A - CORE ............................................. 11	3.4. Value Range Alternatives: %c##-## .........................7
	6.1 CORE RULES ................................................... 11	3.5. Sequence Group: (Rule1 Rule2) .............................8
	6.2 COMMON ENCODING .............................................. 12	3.6. Variable Repetition: *Rule ................................8
		3.7. Specific Repetition: nRule ................................9
	7. ACKNOWLEDGMENTS ............................................... 12	3.8. Optional Sequence: [RULE] .................................9
		3.9. Comment: ; Comment ........................................9
	8. REFERENCES .................................................... 13	3.10. Operator Precedence .......................................9
		4. ABNF DEFINITION OF ABNF ........................................10
	9. CONTACT ....................................................... 13	5. SECURITY CONSIDERATIONS ........................................11
		6. References .....................................................11
	10. FULL COPYRIGHT STATEMENT ..................................... 14	6.1. Normative References ......................................11
		6.2. Informative References ....................................11
		Appendix A. ACKNOWLEDGEMENTS .....................................13
		Appendix B. APPENDIX - CORE ABNF OF ABNF .........................13
		B.1. Core Rules ...............................................13
		B.2. Common Encoding ..........................................14


	1. INTRODUCTION	1. INTRODUCTION


	Internet technical specifications often need to define a format	Internet technical specifications often need to define a formal
	syntax and are free to employ whatever notation their authors deem	syntax and are free to employ whatever notation their authors deem
	useful. Over the years, a modified version of Backus-Naur Form	useful. Over the years, a modified version of Backus-Naur Form
	(BNF), called Augmented BNF (ABNF), has been popular among many	(BNF), called Augmented BNF (ABNF), has been popular among many
	Internet specifications. It balances compactness and simplicity,	Internet specifications. It balances compactness and simplicity,
	with reasonable representational power. In the early days of the	with reasonable representational power. In the early days of the
	Arpanet, each specification contained its own definition of ABNF.	Arpanet, each specification contained its own definition of ABNF.

	This included the email specifications, RFC733 and then RFC822 which	This included the email specifications, [RFC733] and then [RFC822],
	have come to be the common citations for defining ABNF. The current	which came to be the common citations for defining ABNF. The current
	document separates out that definition, to permit selective	document separates those definitions to permit selective reference.
	reference. Predictably, it also provides some modifications and	Predictably, it also provides some modifications and enhancements.
	enhancements.

	The differences between standard BNF and ABNF involve naming rules,	The differences between standard BNF and ABNF involve naming rules,
	repetition, alternatives, order-independence, and value ranges.	repetition, alternatives, order-independence, and value ranges.

	Appendix A (Core) supplies rule definitions and encoding for a core	Appendix B supplies rule definitions and encoding for a core lexical
	lexical analyzer of the type common to several Internet	analyzer of the type common to several Internet specifications. It
	specifications. It is provided as a convenience and is otherwise	is provided as a convenience and is otherwise separate from the meta
	separate from the meta language defined in the body of this document,	language defined in the body of this document, and separate from its
	and separate from its formal status.	formal status.


	2. RULE DEFINITION	Changes since [RFC2234]:


	2.1 Rule Naming	In Section 3.7, the phrase: "That is, exactly <N> occurrences of
		<element>." was corrected to: "That is, exactly <n> occurrences of
		<element>."

		Some continuation comment lines needed to be corrected to begin
		with comment character (";").

		2. RULE DEFINITION

		2.1. Rule Naming

	The name of a rule is simply the name itself; that is, a sequence of	The name of a rule is simply the name itself; that is, a sequence of

	characters, beginning with an alphabetic character, and followed by	characters, beginning with an alphabetic character, and followed by a
	a combination of alphabetics, digits and hyphens (dashes).	combination of alphabetics, digits, and hyphens (dashes).

		NOTE:


	NOTE: Rule names are case-insensitive	Rule names are case-insensitive


	The names <rulename>, <Rulename>, <RULENAME> and <rUlENamE> all refer	The names <rulename>, <Rulename>, <RULENAME>, and <rUlENamE> all
	to the same rule.	refer to the same rule.


	Unlike original BNF, angle brackets ("<", ">") are not required.	Unlike original BNF, angle brackets ("<", ">") are not required.
	However, angle brackets may be used around a rule name whenever their	However, angle brackets may be used around a rule name whenever their

	presence will facilitate discerning the use of a rule name. This is	presence facilitates in discerning the use of a rule name. This is
	typically restricted to rule name references in free-form prose, or	typically restricted to rule name references in free-form prose, or
	to distinguish partial rules that combine into a string not separated	to distinguish partial rules that combine into a string not separated
	by white space, such as shown in the discussion about repetition,	by white space, such as shown in the discussion about repetition,
	below.	below.


	2.2 Rule Form	2.2. Rule Form

	A rule is defined by the following sequence:	A rule is defined by the following sequence:


	name = elements crlf	name = elements crlf

	where <name> is the name of the rule, <elements> is one or more rule	where <name> is the name of the rule, <elements> is one or more rule

	names or terminal specifications and <crlf> is the end-of- line	names or terminal specifications, and <crlf> is the end-of-line
	indicator, carriage return followed by line feed. The equal sign	indicator (carriage return followed by line feed). The equal sign
	separates the name from the definition of the rule. The elements	separates the name from the definition of the rule. The elements
	form a sequence of one or more rule names and/or value definitions,	form a sequence of one or more rule names and/or value definitions,

	combined according to the various operators, defined in this	combined according to the various operators defined in this document,
	document, such as alternative and repetition.	such as alternative and repetition.

	For visual ease, rule definitions are left aligned. When a rule	For visual ease, rule definitions are left aligned. When a rule
	requires multiple lines, the continuation lines are indented. The	requires multiple lines, the continuation lines are indented. The
	left alignment and indentation are relative to the first lines of the	left alignment and indentation are relative to the first lines of the
	ABNF rules and need not match the left margin of the document.	ABNF rules and need not match the left margin of the document.


	2.3 Terminal Values	2.3. Terminal Values

	Rules resolve into a string of terminal values, sometimes called	Rules resolve into a string of terminal values, sometimes called

	characters. In ABNF a character is merely a non-negative integer.	characters. In ABNF, a character is merely a non-negative integer.
	In certain contexts a specific mapping (encoding) of values into a	In certain contexts, a specific mapping (encoding) of values into a
	character set (such as ASCII) will be specified.	character set (such as ASCII) will be specified.


	Terminals are specified by one or more numeric characters with the	Terminals are specified by one or more numeric characters, with the
	base interpretation of those characters indicated explicitly. The	base interpretation of those characters indicated explicitly. The
	following bases are currently defined:	following bases are currently defined:


	b = binary	b = binary


	d = decimal	d = decimal


	x = hexadecimal	x = hexadecimal

	Hence:	Hence:


	CR = %d13	CR = %d13


	CR = %x0D	CR = %x0D

	respectively specify the decimal and hexadecimal representation of	respectively specify the decimal and hexadecimal representation of
	[US-ASCII] for carriage return.	[US-ASCII] for carriage return.

	A concatenated string of such values is specified compactly, using a	A concatenated string of such values is specified compactly, using a

	period (".") to indicate separation of characters within that value.	period (".") to indicate a separation of characters within that
	Hence:	value. Hence:


	CRLF = %d13.10	CRLF = %d13.10


	ABNF permits specifying literal text string directly, enclosed in	ABNF permits the specification of literal text strings directly,
	quotation-marks. Hence:	enclosed in quotation-marks. Hence:


	command = "command string"	command = "command string"

	Literal text strings are interpreted as a concatenated set of	Literal text strings are interpreted as a concatenated set of
	printable characters.	printable characters.


	NOTE: ABNF strings are case-insensitive and	NOTE:
	the character set for these strings is us-ascii.
		ABNF strings are case-insensitive and the character set for these
		strings is us-ascii.

	Hence:	Hence:


	rulename = "abc"	rulename = "abc"

	and:	and:


	rulename = "aBc"	rulename = "aBc"


	will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC" and "ABC".	will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and
		"ABC".


	To specify a rule which IS case SENSITIVE,	To specify a rule that IS case SENSITIVE, specify the characters
	specify the characters individually.	individually.

	For example:	For example:


	rulename = %d97 %d98 %d99	rulename = %d97 %d98 %d99

	or	or


	rulename = %d97.98.99	rulename = %d97.98.99


	will match only the string which comprises only lowercased	will match only the string that comprises only the lowercased
	characters, abc.	characters, abc.


	2.4 External Encodings	2.4. External Encodings

	External representations of terminal value characters will vary	External representations of terminal value characters will vary
	according to constraints in the storage or transmission environment.	according to constraints in the storage or transmission environment.
	Hence, the same ABNF-based grammar may have multiple external	Hence, the same ABNF-based grammar may have multiple external
	encodings, such as one for a 7-bit US-ASCII environment, another for	encodings, such as one for a 7-bit US-ASCII environment, another for

	a binary octet environment and still a different one when 16-bit	a binary octet environment, and still a different one when 16-bit
	Unicode is used. Encoding details are beyond the scope of ABNF,	Unicode is used. Encoding details are beyond the scope of ABNF,
	although Appendix A (Core) provides definitions for a 7-bit US-ASCII	although Appendix A (Core) provides definitions for a 7-bit US-ASCII
	environment as has been common to much of the Internet.	environment as has been common to much of the Internet.

	By separating external encoding from the syntax, it is intended that	By separating external encoding from the syntax, it is intended that
	alternate encoding environments can be used for the same syntax.	alternate encoding environments can be used for the same syntax.


	3. OPERATORS	3. OPERATORS


	3.1 Concatenation Rule1 Rule2	3.1. Concatenation: Rule1 Rule2


	A rule can define a simple, ordered string of values -- i.e., a	A rule can define a simple, ordered string of values (i.e., a
	concatenation of contiguous characters -- by listing a sequence of	concatenation of contiguous characters) by listing a sequence of rule
	rule names. For example:	names. For example:


	foo = %x61 ; a	foo = %x61 ; a


	bar = %x62 ; b	bar = %x62 ; b


	mumble = foo bar foo	mumble = foo bar foo


	So that the rule <mumble> matches the lowercase string "aba".	So that the rule <mumble> matches the lowercase string "aba".


	LINEAR WHITE SPACE: Concatenation is at the core of the ABNF	LINEAR WHITE SPACE: Concatenation is at the core of the ABNF parsing
	parsing model. A string of contiguous characters (values) is	model. A string of contiguous characters (values) is parsed
	parsed according to the rules defined in ABNF. For Internet	according to the rules defined in ABNF. For Internet specifications,
	specifications, there is some history of permitting linear white	there is some history of permitting linear white space (space and
	space (space and horizontal tab) to be freelyPand	horizontal tab) to be freely and implicitly interspersed around major
	implicitlyPinterspersed around major constructs, such as	constructs, such as delimiting special characters or atomic strings.
	delimiting special characters or atomic strings.


	NOTE: This specification for ABNF does not	NOTE:
	provide for implicit specification of linear white
	space.


	Any grammar which wishes to permit linear white space around	This specification for ABNF does not provide for implicit
		specification of linear white space.

		Any grammar that wishes to permit linear white space around
	delimiters or string segments must specify it explicitly. It is	delimiters or string segments must specify it explicitly. It is
	often useful to provide for such white space in "core" rules that are	often useful to provide for such white space in "core" rules that are
	then used variously among higher-level rules. The "core" rules might	then used variously among higher-level rules. The "core" rules might
	be formed into a lexical analyzer or simply be part of the main	be formed into a lexical analyzer or simply be part of the main
	ruleset.	ruleset.


	3.2 Alternatives Rule1 / Rule2	3.2. Alternatives: Rule1 / Rule2


	Elements separated by forward slash ("/") are alternatives.	Elements separated by a forward slash ("/") are alternatives.
	Therefore,	Therefore,


	foo / bar	foo / bar

	will accept <foo> or <bar>.	will accept <foo> or <bar>.


	NOTE: A quoted string containing alphabetic	NOTE:
	characters is special form for specifying alternative
	characters and is interpreted as a non-terminal	A quoted string containing alphabetic characters is a special form
	representing the set of combinatorial strings with the	for specifying alternative characters and is interpreted as a
	contained characters, in the specified order but with	non-terminal representing the set of combinatorial strings with
	any mixture of upper and lower case..	the contained characters, in the specified order but with any
		mixture of upper and lower case.


	3.3 Incremental Alternatives Rule1 =/ Rule2	3.3. Incremental Alternatives: Rule1 =/ Rule2

	It is sometimes convenient to specify a list of alternatives in	It is sometimes convenient to specify a list of alternatives in
	fragments. That is, an initial rule may match one or more	fragments. That is, an initial rule may match one or more
	alternatives, with later rule definitions adding to the set of	alternatives, with later rule definitions adding to the set of

	alternatives. This is particularly useful for otherwise- independent	alternatives. This is particularly useful for otherwise, independent
	specifications which derive from the same parent rule set, such as	specifications that derive from the same parent rule set, such as
	often occurs with parameter lists. ABNF permits this incremental	often occurs with parameter lists. ABNF permits this incremental
	definition through the construct:	definition through the construct:


	oldrule =/ additional-alternatives	oldrule =/ additional-alternatives

	So that the rule set	So that the rule set


	ruleset = alt1 / alt2	ruleset = alt1 / alt2


	ruleset =/ alt3	ruleset =/ alt3


	ruleset =/ alt4 / alt5	ruleset =/ alt4 / alt5

	is the same as specifying	is the same as specifying


	ruleset = alt1 / alt2 / alt3 / alt4 / alt5	ruleset = alt1 / alt2 / alt3 / alt4 / alt5


	3.4 Value Range Alternatives %c##-##	3.4. Value Range Alternatives: %c##-##

	A range of alternative numeric values can be specified compactly,	A range of alternative numeric values can be specified compactly,
	using dash ("-") to indicate the range of alternative values. Hence:	using dash ("-") to indicate the range of alternative values. Hence:


	DIGIT = %x30-39	DIGIT = %x30-39

	is equivalent to:	is equivalent to:


	DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" /	DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" /


	"7" / "8" / "9"	"7" / "8" / "9"


	Concatenated numeric values and numeric value ranges can not be	Concatenated numeric values and numeric value ranges cannot be
	specified in the same string. A numeric value may use the dotted	specified in the same string. A numeric value may use the dotted
	notation for concatenation or it may use the dash notation to specify	notation for concatenation or it may use the dash notation to specify

	one value range. Hence, to specify one printable character, between	one value range. Hence, to specify one printable character between
	end of line sequences, the specification could be:	end of line sequences, the specification could be:


	char-line = %x0D.0A %x20-7E %x0D.0A	char-line = %x0D.0A %x20-7E %x0D.0A


	3.5 Sequence Group (Rule1 Rule2)	3.5. Sequence Group: (Rule1 Rule2)

	Elements enclosed in parentheses are treated as a single element,	Elements enclosed in parentheses are treated as a single element,

	whose contents are STRICTLY ORDERED. Thus,	whose contents are STRICTLY ORDERED. Thus,


	elem (foo / bar) blat	elem (foo / bar) blat


	which matches (elem foo blat) or (elem bar blat).	matches (elem foo blat) or (elem bar blat), and


	elem foo / bar blat	elem foo / bar blat

	matches (elem foo) or (bar blat).	matches (elem foo) or (bar blat).


	NOTE: It is strongly advised to use grouping	NOTE:
	notation, rather than to rely on proper reading of
	"bare" alternations, when alternatives consist of
	multiple rule names or literals.


	Hence it is recommended that instead of the above form, the form:	It is strongly advised that grouping notation be used, rather than
		relying on the proper reading of "bare" alternations, when
		alternatives consist of multiple rule names or literals.

		Hence, it is recommended that the following form be used:

	(elem foo) / (bar blat)	(elem foo) / (bar blat)


	be used. It will avoid misinterpretation by casual readers.	It will avoid misinterpretation by casual readers.

	The sequence group notation is also used within free text to set off	The sequence group notation is also used within free text to set off
	an element sequence from the prose.	an element sequence from the prose.


	3.6 Variable Repetition *Rule	3.6. Variable Repetition: *Rule


	The operator "*" preceding an element indicates repetition. The full	The operator "*" preceding an element indicates repetition. The full
	form is:	form is:


	<a>*<b>element	<a>*<b>element

	where <a> and <b> are optional decimal values, indicating at least	where <a> and <b> are optional decimal values, indicating at least

	<a> and at most <b> occurrences of element.	<a> and at most <b> occurrences of the element.

	Default values are 0 and infinity so that *<element> allows any	Default values are 0 and infinity so that *<element> allows any

	number, including zero; 1*<element> requires at least one;	number, including zero; 1*<element> requires at least one;
	33<element> allows exactly 3 and 12<element> allows one or two.	33<element> allows exactly 3 and 12<element> allows one or two.


	3.7 Specific Repetition nRule	3.7. Specific Repetition: nRule

	A rule of the form:	A rule of the form:


	<n>element	<n>element

	is equivalent to	is equivalent to


	<n>*<n>element	<n>*<n>element


	That is, exactly <N> occurrences of <element>. Thus 2DIGIT is a	That is, exactly <n> occurrences of <element>. Thus, 2DIGIT is a 2-
	2-digit number, and 3ALPHA is a string of three alphabetic	digit number, and 3ALPHA is a string of three alphabetic characters.
	characters.


	3.8 Optional Sequence [RULE]	3.8. Optional Sequence: [RULE]

	Square brackets enclose an optional element sequence:	Square brackets enclose an optional element sequence:


	[foo bar]	[foo bar]

	is equivalent to	is equivalent to


	*1(foo bar).	*1(foo bar).


	3.9 ; Comment	3.9. Comment: ; Comment

	A semi-colon starts a comment that continues to the end of line.	A semi-colon starts a comment that continues to the end of line.
	This is a simple way of including useful notes in parallel with the	This is a simple way of including useful notes in parallel with the
	specifications.	specifications.


	3.10 Operator Precedence	3.10. Operator Precedence

	The various mechanisms described above have the following precedence,	The various mechanisms described above have the following precedence,

	from highest (binding tightest) at the top, to lowest and loosest at	from highest (binding tightest) at the top, to lowest (loosest) at
	the bottom:	the bottom:


	Strings, Names formation	Strings, Names formation
	Comment
	Value range	Comment
	Repetition
	Grouping, Optional	Value range
	Concatenation
	Alternative	Repetition

		Grouping, Optional

		Concatenation

		Alternative

		Use of the alternative operator, freely mixed with concatenations,
		can be confusing.


	Use of the alternative operator, freely mixed with concatenations can	Again, it is recommended that the grouping operator be used to
	be confusing.	make explicit concatenation groups.


	Again, it is recommended that the grouping operator be used to	4. ABNF DEFINITION OF ABNF
	make explicit concatenation groups.


	4. ABNF DEFINITION OF ABNF	NOTES:


	This syntax uses the rules provided in Appendix A (Core).	1. This syntax requires a formatting of rules that is relatively
		strict. Hence, the version of a ruleset included in a
		specification might need preprocessing to ensure that it can be
		interpreted by an ABNF parser.


	rulelist = 1( rule / (c-wsp c-nl) )	2. This syntax uses the rules provided in Appendix B (Core).


	rule = rulename defined-as elements c-nl	rulelist = 1( rule / (c-wsp c-nl) )
	; continues if next line starts
	; with white space


	rulename = ALPHA *(ALPHA / DIGIT / "-")	rule = rulename defined-as elements c-nl
		; continues if next line starts
		; with white space


	defined-as = c-wsp ("=" / "=/") c-wsp	rulename = ALPHA *(ALPHA / DIGIT / "-")
	; basic rules definition and
	; incremental alternatives


	elements = alternation *c-wsp	defined-as = c-wsp ("=" / "=/") c-wsp
		; basic rules definition and
		; incremental alternatives


	c-wsp = WSP / (c-nl WSP)	elements = alternation *c-wsp


	c-nl = comment / CRLF	c-wsp = WSP / (c-nl WSP)
	; comment or newline


	comment = ";" *(WSP / VCHAR) CRLF	c-nl = comment / CRLF
		; comment or newline


	alternation = concatenation	comment = ";" *(WSP / VCHAR) CRLF
	(c-wsp "/" *c-wsp concatenation)


	concatenation = repetition (1c-wsp repetition)	alternation = concatenation
		(c-wsp "/" *c-wsp concatenation)


	repetition = [repeat] element	concatenation = repetition (1c-wsp repetition)


	repeat = 1DIGIT / (DIGIT "" DIGIT)	repetition = [repeat] element


	element = rulename / group / option /	repeat = 1DIGIT / (DIGIT "" DIGIT)
	char-val / num-val / prose-val	element = rulename / group / option /
		char-val / num-val / prose-val


	group = "(" c-wsp alternation c-wsp ")"	group = "(" c-wsp alternation c-wsp ")"


	option = "[" c-wsp alternation c-wsp "]"	option = "[" c-wsp alternation c-wsp "]"


	char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE	char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
	; quoted string of SP and VCHAR	; quoted string of SP and VCHAR
	without DQUOTE	; without DQUOTE


	num-val = "%" (bin-val / dec-val / hex-val)	num-val = "%" (bin-val / dec-val / hex-val)


	bin-val = "b" 1*BIT	bin-val = "b" 1*BIT
	[ 1("." 1BIT) / ("-" 1*BIT) ]	[ 1("." 1BIT) / ("-" 1*BIT) ]
	; series of concatenated bit values	; series of concatenated bit values
	; or single ONEOF range	; or single ONEOF range


	dec-val = "d" 1*DIGIT	dec-val = "d" 1*DIGIT
	[ 1("." 1DIGIT) / ("-" 1*DIGIT) ]	[ 1("." 1DIGIT) / ("-" 1*DIGIT) ]


	hex-val = "x" 1*HEXDIG	hex-val = "x" 1*HEXDIG
	[ 1("." 1HEXDIG) / ("-" 1*HEXDIG) ]	[ 1("." 1HEXDIG) / ("-" 1*HEXDIG) ]


	prose-val = "<" *(%x20-3D / %x3F-7E) ">"	prose-val = "<" *(%x20-3D / %x3F-7E) ">"
	; bracketed string of SP and VCHAR	; bracketed string of SP and VCHAR
	without angles	; without angles
	; prose description, to be used as	; prose description, to be used as
	last resort	; last resort


	5. SECURITY CONSIDERATIONS	5. SECURITY CONSIDERATIONS

	Security is truly believed to be irrelevant to this document.	Security is truly believed to be irrelevant to this document.


	6. APPENDIX A - CORE	6. References

		6.1. Normative References

		[US-ASCII] American National Standards Institute, "Coded Character
		Set -- 7-bit American Standard Code for Information
		Interchange", ANSI X3.4, 1986.

		6.2. Informative References

		[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
		Specifications: ABNF", RFC 2234, November 1997.

		[RFC733] Crocker, D., Vittal, J., Pogran, K., and D. Henderson,
		"Standard for the format of ARPA network text messages",
		RFC 733, November 1977.

		[RFC822] Crocker, D., "Standard for the format of ARPA Internet
		text messages", STD 11, RFC 822, August 1982.

		Appendix A. ACKNOWLEDGEMENTS

		The syntax for ABNF was originally specified in RFC 733. Ken L.
		Harrenstien, of SRI International, was responsible for re-coding the
		BNF into an augmented BNF that makes the representation smaller and
		easier to understand.

		This recent project began as a simple effort to cull out the portion
		of RFC 822 that has been repeatedly cited by non-email specification
		writers, namely the description of augmented BNF. Rather than simply
		and blindly converting the existing text into a separate document,
		the working group chose to give careful consideration to the
		deficiencies, as well as benefits, of the existing specification and
		related specifications made available over the last 15 years, and
		therefore to pursue enhancement. This turned the project into
		something rather more ambitious than was first intended.
		Interestingly, the result is not massively different from that
		original, although decisions, such as removing the list notation,
		came as a surprise.

		This "separated" version of the specification was part of the DRUMS
		working group, with significant contributions from Jerome Abela,
		Harald Alvestrand, Robert Elz, Roger Fajman, Aviva Garrett, Tom
		Harsch, Dan Kohn, Bill McQuillan, Keith Moore, Chris Newman, Pete
		Resnick, and Henning Schulzrinne.

		Julian Reschke warrants a special thanks for converting the Draft
		Standard version to XML source form.

		Appendix B. APPENDIX - CORE ABNF OF ABNF

	This Appendix is provided as a convenient core for specific grammars.	This Appendix is provided as a convenient core for specific grammars.
	The definitions may be used as a core set of rules.	The definitions may be used as a core set of rules.


	6.1 Core Rules	B.1. Core Rules


	Certain basic rules are in uppercase, such as SP, HTAB, CRLF,	Certain basic rules are in uppercase, such as SP, HTAB, CRLF, DIGIT,
	DIGIT, ALPHA, etc.	ALPHA, etc.


	ALPHA = %x41-5A / %x61-7A ; A-Z / a-z	ALPHA = %x41-5A / %x61-7A ; A-Z / a-z


	BIT = "0" / "1"	BIT = "0" / "1"


	CHAR = %x01-7F	CHAR = %x01-7F
	; any 7-bit US-ASCII character,	; any 7-bit US-ASCII character,
	excluding NUL	; excluding NUL


	CR = %x0D	CR = %x0D
	; carriage return	; carriage return


	CRLF = CR LF	CRLF = CR LF
	; Internet standard newline	; Internet standard newline


	CTL = %x00-1F / %x7F	CTL = %x00-1F / %x7F
	; controls	; controls


	DIGIT = %x30-39	DIGIT = %x30-39
	; 0-9	; 0-9


	DQUOTE = %x22	DQUOTE = %x22
	; " (Double Quote)	; " (Double Quote)


	HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"	HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"


	HTAB = %x09	HTAB = %x09
	; horizontal tab	; horizontal tab


	LF = %x0A	LF = %x0A
	; linefeed	; linefeed


	LWSP = *(WSP / CRLF WSP)	LWSP = *(WSP / CRLF WSP)
	; linear white space (past newline)	; linear white space (past newline)


	OCTET = %x00-FF	OCTET = %x00-FF
	; 8 bits of data	; 8 bits of data


	SP = %x20	SP = %x20
	; space


	VCHAR = %x21-7E	VCHAR = %x21-7E
	; visible (printing) characters	; visible (printing) characters


	WSP = SP / HTAB	WSP = SP / HTAB
	; white space	; white space


	6.2 Common Encoding	B.2. Common Encoding


	Externally, data are represented as "network virtual ASCII", namely	Externally, data are represented as "network virtual ASCII" (namely,
	7-bit US-ASCII in an 8-bit field, with the high (8th) bit set to	7-bit US-ASCII in an 8-bit field), with the high (8th) bit set to
	zero. A string of values is in "network byte order" with the	zero. A string of values is in "network byte order", in which the
	higher-valued bytes represented on the left-hand side and being sent	higher-valued bytes are represented on the left-hand side and are
	over the network first.	sent over the network first.


	7. ACKNOWLEDGMENTS	Authors' Addresses


	The syntax for ABNF was originally specified in RFC 733. Ken L.	Dave Crocker (editor)
	Harrenstien, of SRI International, was responsible for re-coding the	Brandenburg InternetWorking
	BNF into an augmented BNF that makes the representation smaller and	675 Spruce Dr.
	easier to understand.	Sunnyvale, CA 94086
		US


	This recent project began as a simple effort to cull out the portion	Phone: +1.408.246.8253
	of RFC 822 which has been repeatedly cited by non-email specification	EMail: dcrocker@bbiw.net
	writers, namely the description of augmented BNF. Rather than simply
	and blindly converting the existing text into a separate document,	Paul Overell
	the working group chose to give careful consideration to the	THUS plc.
	deficiencies, as well as benefits, of the existing specification and	1/2 Berkeley Square
	related specifications available over the last 15 years and therefore	99 Berkeley Street
	to pursue enhancement. This turned the project into something rather	Glasgow
	more ambitious than first intended. Interestingly the result is not	G3 7HR
	massively different from that original, although decisions such as	UK
	removing the list notation came as a surprise.
		EMail: paul.overell@thus.net
	The current round of specification was part of the DRUMS working
	group, with significant contributions from Jerome Abela , Harald	Full Copyright Statement
	Alvestrand, Robert Elz, Roger Fajman, Aviva Garrett, Tom Harsch, Dan
	Kohn, Bill McQuillan, Keith Moore, Chris Newman , Pete Resnick and	Copyright (C) The Internet Society (2005).
	Henning Schulzrinne.
		This document is subject to the rights, licenses and restrictions
	8. REFERENCES	contained in BCP 78, and except as set forth therein, the authors
		retain all their rights.
	[US-ASCII] Coded Character Set--7-Bit American Standard Code for
	Information Interchange, ANSI X3.4-1986.	This document and the information contained herein are provided on an
		"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	[RFC733] Crocker, D., Vittal, J., Pogran, K., and D. Henderson,	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
	"Standard for the Format of ARPA Network Text Message," RFC 733,	ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
	November 1977.	INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
		INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	[RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Messages", STD 11, RFC 822, August 1982.
		Intellectual Property
	9. CONTACT
		The IETF takes no position regarding the validity or scope of any
	David H. Crocker Paul Overell	Intellectual Property Rights or other rights that might be claimed to
		pertain to the implementation or use of the technology described in
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	675 Spruce Dr. Dorking Business Park	might or might not be available; nor does it represent that it has
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	Phone: +1 408 246 8253	Copies of IPR disclosures made to the IETF Secretariat and any
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		such proprietary rights by implementers or users of this
	10. Full Copyright Statement	specification can be obtained from the IETF on-line IPR repository at
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	Copyright (C) The Internet Society (1997). All Rights Reserved.
		The IETF invites any interested party to bring to its attention any
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	The limited permissions granted above are perpetual and will not be
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