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svn commit: r582998 - in /labs/webarch/trunk/http/draft-fielding-http:
rfc4234.html rfc4234.xml
Author: fielding
Date: Mon Oct 8 16:22:40 2007
New Revision: 582998
URL: http://svn.apache.org/viewvc?rev=582998&view=rev
Log:
RFC 4234: Augmented BNF for Syntax Specifications: ABNF
Translated from text to XML by Julian Reschke.
Added:
labs/webarch/trunk/http/draft-fielding-http/rfc4234.html (with props)
labs/webarch/trunk/http/draft-fielding-http/rfc4234.xml (with props)
Added: labs/webarch/trunk/http/draft-fielding-http/rfc4234.html
URL: http://svn.apache.org/viewvc/labs/webarch/trunk/http/draft-fielding-http/rfc4234.html?rev=582998&view=auto
==============================================================================
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+</style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyright"><link rel="Chapter" title="1 INTRODUCTION" href="#rfc.section.1"><link rel="Chapter" title="2 RULE DEFINITION" href="#rfc.section.2"><link rel="Chapter" title="3 OPERATORS" href="#rfc.section.3"><link rel="Chapter" title="4 ABNF DEFINITION OF ABNF" href="#rfc.section.4"><link rel="Chapter" title="5 SECURITY CONSIDERATIONS" href="#rfc.section.5"><link rel="Chapter" href="#rfc.section.6" title="6 References"><link rel="Appendix" title="A ACKNOWLEDGEMENTS" href="#rfc.section.A"><link rel="Appendix" title="B APPENDIX - CORE ABNF OF ABNF" href="#rfc.section.B"><link rel="Alternate" title="Authorative ASCII version" href="http://www.ietf.org/rfc/rfc4234.txt"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.346, 2007/10/07 13:54:24, XSLT vendor: SAXON 8.5.1 from Saxonica http://www.saxonica.com/"><meta name="keyword
s" content="ABNF, Augmented, Backus-Naur, Form, electronic, mail"><link rel="schema.DC" href="http://purl.org/dc/elements/1.1/"><meta name="DC.Creator" content="Crocker, D."><meta name="DC.Creator" content="Overell, P."><meta name="DC.Identifier" content="urn:ietf:rfc:4234"><meta name="DC.Date.Issued" scheme="ISO8601" content="2005-10"><meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2234"><meta name="DC.Description.Abstract" content="Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity, with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order- independence, and value ranges. This specification also supplies additional rule definitions and encodin
g for a core lexical analyzer of the type common to several Internet specifications."></head><body><table summary="header information" class="header" border="0" cellpadding="1" cellspacing="1"><tr><td class="header left">Network Working Group</td><td class="header right">D. Crocker, Editor</td></tr><tr><td class="header left">Request for Comments: 4234</td><td class="header right">Brandenburg InternetWorking</td></tr><tr><td class="header left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2234">2234</a></td><td class="header right">P. Overell</td></tr><tr><td class="header left">Category: Standards Track</td><td class="header right">THUS plc.</td></tr><tr><td class="header left"></td><td class="header right">October 2005</td></tr></table><p class="title">Augmented BNF for Syntax Specifications: ABNF</p><h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1><p>This document specifies an Internet standards track protocol for the Internet community, and requ
ests discussion and suggestions for improvements. Please refer to the current edition of the “Internet Official Protocol Standards” (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.</p><h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright © The Internet Society (2005). All Rights Reserved.</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> <p>Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity, with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order- independence, and value ranges. This specification also supplies additional
rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications.</p> <hr class="noprint"><h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li class="tocline0">1. <a href="#rfc.section.1">INTRODUCTION</a></li><li class="tocline0">2. <a href="#rfc.section.2">RULE DEFINITION</a><ul class="toc"><li class="tocline1">2.1. <a href="#rfc.section.2.1">Rule Naming</a></li><li class="tocline1">2.2. <a href="#rfc.section.2.2">Rule Form</a></li><li class="tocline1">2.3. <a href="#rfc.section.2.3">Terminal Values</a></li><li class="tocline1">2.4. <a href="#rfc.section.2.4">External Encodings</a></li></ul></li><li class="tocline0">3. <a href="#rfc.section.3">OPERATORS</a><ul class="toc"><li class="tocline1">3.1. <a href="#rfc.section.3.1">Concatenation: Rule1 Rule2</a
></li><li class="tocline1">3.2. <a href="#Alternatives">Alternatives: Rule1 / Rule2</a></li><li class="tocline1">3.3. <a href="#Incremental">Incremental Alternatives: Rule1 =/ Rule2</a></li><li class="tocline1">3.4. <a href="#Range">Value Range Alternatives: %c##-##</a></li><li class="tocline1">3.5. <a href="#Sequence">Sequence Group: (Rule1 Rule2)</a></li><li class="tocline1">3.6. <a href="#VarRep">Variable Repetition: *Rule</a></li><li class="tocline1">3.7. <a href="#SpecRep">Specific Repetition: nRule</a></li><li class="tocline1">3.8. <a href="#OptSeq">Optional Sequence: [RULE]</a></li><li class="tocline1">3.9. <a href="#Comment">Comment: ; Comment</a></li><li class="tocline1">3.10. <a href="#rfc.section.3.10">Operator Precedence</a></li></ul></li><li class="tocline0">4. <a href="#rfc.section.4">AB
NF DEFINITION OF ABNF</a></li><li class="tocline0">5. <a href="#rfc.section.5">SECURITY CONSIDERATIONS</a></li><li class="tocline0">6. <a href="#rfc.references">References</a><ul class="toc"><li class="tocline1">6.1. <a href="#rfc.references.1">Normative References</a></li><li class="tocline1">6.2. <a href="#rfc.references.2">Informative References</a></li></ul></li><li class="tocline0"><a href="#rfc.authors">Authors' Addresses</a></li><li class="tocline0">A. <a href="#rfc.section.A">ACKNOWLEDGEMENTS</a></li><li class="tocline0">B. <a href="#CORE">APPENDIX - CORE ABNF OF ABNF</a><ul class="toc"><li class="tocline1">B.1. <a href="#rfc.section.B.1">Core Rules</a></li><li class="tocline1">B.2. <a href="#rfc.section.B.2">Common Encoding</a></li></ul></li><li class="tocline0"><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></
li></ul><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> INTRODUCTION</h1><p id="rfc.section.1.p.1">Internet technical specifications often need to define a formal syntax and are free to employ whatever notation their authors deem useful. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. It balances compactness and simplicity, with reasonable representational power. In the early days of the Arpanet, each specification contained its own definition of ABNF. This included the email specifications, <a href="#RFC733"><cite title="Standard for the format of ARPA network text messages">[RFC733]</cite></a> and then <a href="#RFC822"><cite title="Standard for the format of ARPA Internet text messages">[RFC822]</cite></a>, which came to be the common citations for defining ABNF. The current document separates those definitions to permit selective reference. Predictably,
it also provides some modifications and enhancements.</p><p id="rfc.section.1.p.2">The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. <a href="#CORE" title="APPENDIX - CORE ABNF OF ABNF">Appendix B</a> supplies rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. It is provided as a convenience and is otherwise separate from the meta language defined in the body of this document, and separate from its formal status. </p><dl><dt>Changes since [RFC2234]:</dt><dd>In <a href="#SpecRep" title="Specific Repetition: nRule">Section 3.7</a>, the phrase: "That is, exactly <N> occurrences of <element>." was corrected to: "That is, exactly <n> occurrences of <element>."</dd><dd>Some continuation comment lines needed to be corrected to begin with comment character (";").</dd></dl><h1 id="rfc.section.2"><a href="#rf
c.section.2">2.</a> RULE DEFINITION</h1><h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1.</a> Rule Naming</h2><p id="rfc.section.2.1.p.1">The name of a rule is simply the name itself; that is, a sequence of characters, beginning with an alphabetic character, and followed by a combination of alphabetics, digits, and hyphens (dashes).</p><p id="rfc.section.2.1.p.2"> </p><dl><dt>NOTE: </dt><dd>Rule names are case-insensitive</dd></dl><p id="rfc.section.2.1.p.3">The names <rulename>, <Rulename>, <RULENAME>, and <rUlENamE> all refer to the same rule.</p><p id="rfc.section.2.1.p.4">Unlike original BNF, angle brackets ("<", ">") are not required. However, angle brackets may be used around a rule name whenever their presence facilitates in discerning the use of a rule name. This is typically restricted to rule name references in free-form prose, or to distinguish partial rules that combine into a string not separated by white space, su
ch as shown in the discussion about repetition, below.</p><h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2.</a> Rule Form</h2><p id="rfc.section.2.2.p.1">A rule is defined by the following sequence:</p><div id="rfc.figure.u.1"></div> <pre class="text">
+ name = elements crlf </pre> <p id="rfc.section.2.2.p.3">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 indicator (carriage return followed by line feed). The equal sign separates the name from the definition of the rule. The elements form a sequence of one or more rule names and/or value definitions, combined according to the various operators defined in this document, such as alternative and repetition.</p><p id="rfc.section.2.2.p.4">For visual ease, rule definitions are left aligned. When a rule requires multiple lines, the continuation lines are indented. 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.</p><h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3.</a> Terminal Values</h2><p id="rfc.section.2.3.p.1">Rules resolve into a string of terminal values, sometimes c
alled characters. In ABNF, a character is merely a non-negative integer. In certain contexts, a specific mapping (encoding) of values into a character set (such as ASCII) will be specified.</p><div id="rfc.figure.u.2"></div> <p>Terminals are specified by one or more numeric characters, with the base interpretation of those characters indicated explicitly. The following bases are currently defined:</p> <pre class="text">
+ b = binary
+
+ d = decimal
+
+ x = hexadecimal </pre> <div id="rfc.figure.u.3"></div> <p>Hence:</p> <pre class="text">
+ CR = %d13
+
+ CR = %x0D </pre> <p>respectively specify the decimal and hexadecimal representation of <a href="#US-ASCII"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[US-ASCII]</cite></a> for carriage return.</p> <div id="rfc.figure.u.4"></div> <p>A concatenated string of such values is specified compactly, using a period (".") to indicate a separation of characters within that value. Hence:</p> <pre class="text">
+ CRLF = %d13.10 </pre> <div id="rfc.figure.u.5"></div> <p>ABNF permits the specification of literal text strings directly, enclosed in quotation-marks. Hence:</p> <pre class="text">
+ command = "command string" </pre> <p id="rfc.section.2.3.p.6">Literal text strings are interpreted as a concatenated set of printable characters.</p><p id="rfc.section.2.3.p.7"> </p><dl><dt>NOTE: </dt><dd>ABNF strings are case-insensitive and the character set for these strings is us-ascii.</dd></dl><div id="rfc.figure.u.6"></div> <p>Hence:</p> <pre class="text">
+ rulename = "abc" </pre> <div id="rfc.figure.u.7"></div> <p>and:</p> <pre class="text">
+ rulename = "aBc"
+</pre> <p>will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and "ABC".</p> <p id="rfc.section.2.3.p.10"> </p><dl class="empty"><dd>To specify a rule that IS case SENSITIVE, specify the characters individually.</dd></dl><div id="rfc.figure.u.8"></div> <p>For example:</p> <pre class="text">
+ rulename = %d97 %d98 %d99
+</pre> <div id="rfc.figure.u.9"></div> <p>or</p> <pre class="text">
+ rulename = %d97.98.99
+</pre> <p>will match only the string that comprises only the lowercased characters, abc.</p> <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4.</a> External Encodings</h2><p id="rfc.section.2.4.p.1">External representations of terminal value characters will vary according to constraints in the storage or transmission environment. Hence, the same ABNF-based grammar may have multiple external 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 Unicode is used. Encoding details are beyond the scope of ABNF, although Appendix A (Core) provides definitions for a 7-bit US-ASCII environment as has been common to much of the Internet.</p><p id="rfc.section.2.4.p.2">By separating external encoding from the syntax, it is intended that alternate encoding environments can be used for the same syntax.</p><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> OPERATORS</h1><h2 id="rfc.secti
on.3.1"><a href="#rfc.section.3.1">3.1.</a> Concatenation: Rule1 Rule2</h2><p id="rfc.section.3.1.p.1">A rule can define a simple, ordered string of values (i.e., a concatenation of contiguous characters) by listing a sequence of rule names. For example:</p><div id="rfc.figure.u.10"></div> <pre class="text">
+ foo = %x61 ; a
+
+ bar = %x62 ; b
+
+ mumble = foo bar foo </pre> <p id="rfc.section.3.1.p.3">So that the rule <mumble> matches the lowercase string "aba".</p><p id="rfc.section.3.1.p.4">LINEAR WHITE SPACE: Concatenation is at the core of the ABNF parsing model. A string of contiguous characters (values) is parsed according to the rules defined in ABNF. For Internet specifications, there is some history of permitting linear white space (space and horizontal tab) to be freely and implicitly interspersed around major constructs, such as delimiting special characters or atomic strings.</p><p id="rfc.section.3.1.p.5">NOTE: </p><dl class="empty"><dd>This specification for ABNF does not provide for implicit specification of linear white space.</dd></dl><p id="rfc.section.3.1.p.6">Any grammar that wishes to permit linear white space around delimiters or string segments must specify it explicitly. It is often useful to provide for such white space in "core" rules that are then used variously among high
er-level rules. The "core" rules might be formed into a lexical analyzer or simply be part of the main ruleset.</p><h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2.</a> <a id="Alternatives" href="#Alternatives">Alternatives: Rule1 / Rule2</a></h2><p id="rfc.section.3.2.p.1">Elements separated by a forward slash ("/") are alternatives. Therefore,</p><div id="rfc.figure.u.11"></div> <pre class="text">
+ foo / bar
+</pre> <p>will accept <foo> or <bar>.</p> <p id="rfc.section.3.2.p.3"> </p><dl><dt>NOTE: </dt><dd>A quoted string containing alphabetic characters is a special form for specifying alternative characters and is interpreted as a non-terminal representing the set of combinatorial strings with the contained characters, in the specified order but with any mixture of upper and lower case.</dd></dl><h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3.</a> <a id="Incremental" href="#Incremental">Incremental Alternatives: Rule1 =/ Rule2</a></h2><p id="rfc.section.3.3.p.1">It is sometimes convenient to specify a list of alternatives in fragments. That is, an initial rule may match one or more alternatives, with later rule definitions adding to the set of alternatives. This is particularly useful for otherwise, independent specifications that derive from the same parent rule set, such as often occurs with parameter lists. ABNF permits this incremental definition t
hrough the construct:</p><div id="rfc.figure.u.12"></div> <pre class="text">
+ oldrule =/ additional-alternatives </pre> <div id="rfc.figure.u.13"></div> <p>So that the rule set</p> <pre class="text">
+ ruleset = alt1 / alt2
+
+ ruleset =/ alt3
+
+ ruleset =/ alt4 / alt5 </pre> <div id="rfc.figure.u.14"></div> <p>is the same as specifying</p> <pre class="text">
+ ruleset = alt1 / alt2 / alt3 / alt4 / alt5 </pre> <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4.</a> <a id="Range" href="#Range">Value Range Alternatives: %c##-##</a></h2><div id="rfc.figure.u.15"></div> <p>A range of alternative numeric values can be specified compactly, using dash ("-") to indicate the range of alternative values. Hence:</p> <pre class="text">
+ DIGIT = %x30-39 </pre> <div id="rfc.figure.u.16"></div> <p>is equivalent to:</p> <pre class="text">
+ DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" /
+
+ "7" / "8" / "9" </pre> <div id="rfc.figure.u.17"></div> <p>Concatenated numeric values and numeric value ranges cannot be specified in the same string. A numeric value may use the dotted notation for concatenation or it may use the dash notation to specify one value range. Hence, to specify one printable character between end of line sequences, the specification could be:</p> <pre class="text">
+ char-line = %x0D.0A %x20-7E %x0D.0A </pre> <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5.</a> <a id="Sequence" href="#Sequence">Sequence Group: (Rule1 Rule2)</a></h2><div id="rfc.figure.u.18"></div> <p>Elements enclosed in parentheses are treated as a single element, whose contents are STRICTLY ORDERED. Thus,</p> <pre class="text">
+ elem (foo / bar) blat
+</pre> <p>matches (elem foo blat) or (elem bar blat), and</p> <div id="rfc.figure.u.19"></div> <pre class="text">
+ elem foo / bar blat
+</pre> <p>matches (elem foo) or (bar blat).</p> <p id="rfc.section.3.5.p.3"> </p><dl><dt>NOTE: </dt><dd>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.</dd></dl><div id="rfc.figure.u.20"></div> <p>Hence, it is recommended that the following form be used:</p> <pre class="text">
+ (elem foo) / (bar blat)
+</pre> <p>It will avoid misinterpretation by casual readers.</p> <p id="rfc.section.3.5.p.5">The sequence group notation is also used within free text to set off an element sequence from the prose.</p><h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6.</a> <a id="VarRep" href="#VarRep">Variable Repetition: *Rule</a></h2><div id="rfc.figure.u.21"></div> <p>The operator "*" preceding an element indicates repetition. The full form is:</p> <pre class="text">
+ <a>*<b>element
+</pre> <p>where <a> and <b> are optional decimal values, indicating at least <a> and at most <b> occurrences of the element.</p> <p id="rfc.section.3.6.p.2">Default values are 0 and infinity so that *<element> allows any number, including zero; 1*<element> requires at least one; 3*3<element> allows exactly 3 and 1*2<element> allows one or two.</p><h2 id="rfc.section.3.7"><a href="#rfc.section.3.7">3.7.</a> <a id="SpecRep" href="#SpecRep">Specific Repetition: nRule</a></h2><div id="rfc.figure.u.22"></div> <p>A rule of the form:</p> <pre class="text">
+ <n>element </pre> <div id="rfc.figure.u.23"></div> <p>is equivalent to</p> <pre class="text">
+ <n>*<n>element </pre> <p id="rfc.section.3.7.p.3">That is, exactly <n> occurrences of <element>. Thus, 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters.</p><h2 id="rfc.section.3.8"><a href="#rfc.section.3.8">3.8.</a> <a id="OptSeq" href="#OptSeq">Optional Sequence: [RULE]</a></h2><div id="rfc.figure.u.24"></div> <p>Square brackets enclose an optional element sequence:</p> <pre class="text">
+ [foo bar] </pre> <div id="rfc.figure.u.25"></div> <p>is equivalent to</p> <pre class="text">
+ *1(foo bar). </pre> <h2 id="rfc.section.3.9"><a href="#rfc.section.3.9">3.9.</a> <a id="Comment" href="#Comment">Comment: ; Comment</a></h2><p id="rfc.section.3.9.p.1">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 specifications.</p><h2 id="rfc.section.3.10"><a href="#rfc.section.3.10">3.10.</a> Operator Precedence</h2><p id="rfc.section.3.10.p.1">The various mechanisms described above have the following precedence, from highest (binding tightest) at the top, to lowest (loosest) at the bottom: </p><dl class="empty"><dd>Strings, Names formation</dd><dd>Comment</dd><dd>Value range</dd><dd>Repetition</dd><dd>Grouping, Optional</dd><dd>Concatenation</dd><dd>Alternative</dd></dl><p id="rfc.section.3.10.p.2">Use of the alternative operator, freely mixed with concatenations, can be confusing.</p><p id="rfc.section.3.10.p.3"> </p><dl class="empty"><dd>Again, it is recommended that
the grouping operator be used to make explicit concatenation groups.</dd></dl><h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> ABNF DEFINITION OF ABNF</h1><p id="rfc.section.4.p.1"> </p><dl><dt>NOTES:</dt><dd> <ol><li>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.</li><li>This syntax uses the rules provided in <a href="#CORE" title="APPENDIX - CORE ABNF OF ABNF">Appendix B</a> (Core).</li></ol> </dd></dl><div id="rfc.figure.u.26"></div> <pre class="inline">
+ rulelist = 1*( rule / (*c-wsp c-nl) )
+
+ rule = rulename defined-as elements c-nl
+ ; continues if next line starts
+ ; with white space
+
+ rulename = ALPHA *(ALPHA / DIGIT / "-")
+
+ defined-as = *c-wsp ("=" / "=/") *c-wsp
+ ; basic rules definition and
+ ; incremental alternatives
+
+ elements = alternation *c-wsp
+
+ c-wsp = WSP / (c-nl WSP)
+
+ c-nl = comment / CRLF
+ ; comment or newline
+
+ comment = ";" *(WSP / VCHAR) CRLF
+
+ alternation = concatenation
+ *(*c-wsp "/" *c-wsp concatenation)
+
+ concatenation = repetition *(1*c-wsp repetition)
+
+ repetition = [repeat] element
+
+ repeat = 1*DIGIT / (*DIGIT "*" *DIGIT)
+
+ element = rulename / group / option /
+ char-val / num-val / prose-val
+
+ group = "(" *c-wsp alternation *c-wsp ")"
+
+ option = "[" *c-wsp alternation *c-wsp "]"
+
+ char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
+ ; quoted string of SP and VCHAR
+ ; without DQUOTE
+
+ num-val = "%" (bin-val / dec-val / hex-val)
+
+ bin-val = "b" 1*BIT
+ [ 1*("." 1*BIT) / ("-" 1*BIT) ]
+ ; series of concatenated bit values
+ ; or single ONEOF range
+
+ dec-val = "d" 1*DIGIT
+ [ 1*("." 1*DIGIT) / ("-" 1*DIGIT) ]
+
+ hex-val = "x" 1*HEXDIG
+ [ 1*("." 1*HEXDIG) / ("-" 1*HEXDIG) ]
+
+ prose-val = "<" *(%x20-3D / %x3F-7E) ">"
+ ; bracketed string of SP and VCHAR
+ ; without angles
+ ; prose description, to be used as
+ ; last resort
+</pre> <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> SECURITY CONSIDERATIONS</h1><p id="rfc.section.5.p.1">Security is truly believed to be irrelevant to this document.</p><h1 id="rfc.references"><a id="rfc.section.6" href="#rfc.section.6">6.</a> References</h1><h2 id="rfc.references.1"><a href="#rfc.section.6.1" id="rfc.section.6.1">6.1.</a> Normative References</h2><table summary="Normative References"> <tr><td class="reference"><b id="US-ASCII">[US-ASCII]</b></td><td class="top">American National Standards
+ Institute, “Coded Character Set -- 7-bit American Standard Code for
+ Information Interchange”, ANSI X3.4, 1986.</td></tr></table><h2 id="rfc.references.2"><a href="#rfc.section.6.2" id="rfc.section.6.2">6.2.</a> Informative References</h2><table summary="Informative References"> <tr><td class="reference"><b id="RFC2234">[RFC2234]</b></td><td class="top">Crocker, D. and P. Overell, “<a href="http://tools.ietf.org/html/rfc2234">Augmented BNF for Syntax Specifications: ABNF</a>”, RFC 2234, November 1997.</td></tr><tr><td class="reference"><b id="RFC733">[RFC733]</b></td><td class="top"><a href="mailto:DCrocker@Rand-Unix" title="The Rand Corporation, Information Sciences
 Department">Crocker, D.</a>, <a href="mailto:Vittal@BBN-TenexD" title="Bolt Beranek and Newman Inc. (BBN)">Vittal, J.</a>, <a href="mailto:Pogran@MIT-Multics" title="Massachusets Institute of Technology (MIT),
 Laboratory for Computer Science">Pogran, K.</a>, and <a href="mail
to:Henderson@BBN-TenexD" title="Bolt Beranek and Newman Inc. (BBN)">D. Henderson</a>, “<a href="http://tools.ietf.org/html/rfc733">Standard for the format of ARPA network text messages</a>”, RFC 733, November 1977.</td></tr><tr><td class="reference"><b id="RFC822">[RFC822]</b></td><td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical
 Engineering">Crocker, D.H.</a>, “<a href="http://tools.ietf.org/html/rfc822">Standard
+ for the format of ARPA Internet text messages</a>”, STD 11, RFC 822, August 1982.</td></tr></table><h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1><address class="vcard"><span class="vcardline"><span class="fn">Dave Crocker</span>
+ (editor)
+ <span class="n hidden"><span class="family-name">Crocker</span><span class="given-name">Dave</span></span></span><span class="org vcardline">Brandenburg InternetWorking</span><span class="adr"><span class="street-address vcardline">675 Spruce Dr.</span><span class="vcardline"><span class="locality">Sunnyvale</span>, <span class="region">CA</span> <span class="postal-code">94086</span></span><span class="country-name vcardline">US</span></span><span class="vcardline tel">Phone: <a href="tel:+1.408.246.8253"><span class="value">+1.408.246.8253</span></a></span><span class="vcardline">EMail: <a href="mailto:dcrocker@bbiw.net"><span class="email">dcrocker@bbiw.net</span></a></span></address><address class="vcard"><span class="vcardline"><span class="fn">Paul Overell</span><span class="n hidden"><span class="family-name">Overell</span><span class="given-name">Paul</span></span></span><span class="org vcardline">THUS plc.</span><span class="adr"><span class="street-ad
dress vcardline">1/2 Berkeley Square, </span><span class="street-address vcardline">99 Berkeley Street</span><span class="vcardline"><span class="locality">Glasgow</span>, <span class="postal-code">G3 7HR</span></span><span class="country-name vcardline">UK</span></span><span class="vcardline">EMail: <a href="mailto:paul.overell@thus.net"><span class="email">paul.overell@thus.net</span></a></span></address><h1 id="rfc.section.A"><a href="#rfc.section.A">A.</a> ACKNOWLEDGEMENTS</h1><p id="rfc.section.A.p.1">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.</p><p id="rfc.section.A.p.2">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 c
onverting 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.</p><p id="rfc.section.A.p.3">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.</p><p id="rfc.section.A.p.4">Julian Reschke warrants a special thanks for converting the Draft Standard version to XML source form.</p><h1 id="rf
c.section.B"><a href="#rfc.section.B">B.</a> <a id="CORE" href="#CORE">APPENDIX - CORE ABNF OF ABNF</a></h1><p id="rfc.section.B.p.1">This Appendix is provided as a convenient core for specific grammars. The definitions may be used as a core set of rules.</p><h2 id="rfc.section.B.1"><a href="#rfc.section.B.1">B.1.</a> Core Rules</h2><p id="rfc.section.B.1.p.1">Certain basic rules are in uppercase, such as SP, HTAB, CRLF, DIGIT, ALPHA, etc.</p><div id="rfc.figure.u.27"></div> <pre class="inline">
+ ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
+
+ BIT = "0" / "1"
+
+ CHAR = %x01-7F
+ ; any 7-bit US-ASCII character,
+ ; excluding NUL
+
+ CR = %x0D
+ ; carriage return
+
+ CRLF = CR LF
+ ; Internet standard newline
+
+ CTL = %x00-1F / %x7F
+ ; controls
+
+ DIGIT = %x30-39
+ ; 0-9
+
+ DQUOTE = %x22
+ ; " (Double Quote)
+
+ HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
+
+ HTAB = %x09
+ ; horizontal tab
+
+ LF = %x0A
+ ; linefeed
+
+ LWSP = *(WSP / CRLF WSP)
+ ; linear white space (past newline)
+
+ OCTET = %x00-FF
+ ; 8 bits of data
+
+ SP = %x20
+
+ VCHAR = %x21-7E
+ ; visible (printing) characters
+
+ WSP = SP / HTAB
+ ; white space
+</pre> <h2 id="rfc.section.B.2"><a href="#rfc.section.B.2">B.2.</a> Common Encoding</h2><p id="rfc.section.B.2.p.1">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 zero. A string of values is in "network byte order", in which the higher-valued bytes are represented on the left-hand side and are sent over the network first.</p><h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1><p>Copyright © The Internet Society (2005).</p><p>This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.</p><p>This document and the information contained herein are provided on an “AS IS” basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.</p><h1><a id="rfc.ipr" href="#rfc.ipr">Intellectual Property</a></h1><p>The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.</p><p>Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such pro
prietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at <<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>>.</p><p>The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at <a href="mailto:ietf-ipr@ietf.org">ietf-ipr@ietf.org</a>.</p><h1>Acknowledgement</h1><p>Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).</p></body></html>
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--- labs/webarch/trunk/http/draft-fielding-http/rfc4234.xml (added)
+++ labs/webarch/trunk/http/draft-fielding-http/rfc4234.xml Mon Oct 8 16:22:40 2007
@@ -0,0 +1,759 @@
+<?xml version="1.0" encoding="utf-8"?>
+<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
+
+<?rfc comments="yes"?>
+<?rfc inline="yes"?>
+<?rfc compact="yes" ?>
+<?rfc subcompact="no" ?>
+<?rfc toc="yes" ?>
+<?rfc tocdepth="2" ?>
+<?rfc tocindent="yes" ?>
+<?rfc symrefs="yes" ?>
+<?rfc sortrefs="yes"?>
+<?rfc iprnotified="no" ?>
+<?rfc-ext sec-no-trailing-dots="yes" ?>
+<?rfc strict="yes" ?>
+<?rfc editing="no" ?>
+<rfc category="std" number="4234" obsoletes="2234">
+ <front>
+ <title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
+ <author fullname="Dave Crocker" initials="D." role="editor"
+ surname="Crocker">
+ <organization>Brandenburg InternetWorking</organization>
+ <address>
+ <postal>
+ <street>675 Spruce Dr.</street>
+ <city>Sunnyvale</city>
+ <region>CA</region>
+ <code>94086</code>
+ <country>US</country>
+ </postal>
+ <phone>+1.408.246.8253</phone>
+ <email>dcrocker@bbiw.net</email>
+ </address>
+ </author>
+ <author fullname="Paul Overell" initials="P." surname="Overell">
+ <organization>THUS plc.</organization>
+ <address>
+ <postal>
+ <street>1/2 Berkeley Square, </street>
+ <street>99 Berkeley Street</street>
+ <city>Glasgow</city>
+ <code>G3 7HR</code>
+ <country>UK</country>
+ </postal>
+ <email>paul.overell@thus.net</email>
+ </address>
+ </author>
+ <date month="October" year="2005"></date>
+ <keyword>ABNF</keyword>
+ <keyword>Augmented</keyword>
+ <keyword>Backus-Naur</keyword>
+ <keyword>Form</keyword>
+ <keyword>electronic</keyword>
+ <keyword>mail</keyword>
+ <abstract>
+ <t>Internet technical specifications often need to define a formal
+ syntax. Over the years, a modified version of Backus-Naur Form
+ (BNF), called Augmented BNF (ABNF), has been popular among many
+ Internet specifications. The current specification documents ABNF.
+ It balances compactness and simplicity, with reasonable
+ representational power. The differences between standard BNF and
+ ABNF involve naming rules, repetition, alternatives, order-
+ independence, and value ranges. This specification also supplies
+ additional rule definitions and encoding for a core lexical analyzer
+ of the type common to several Internet specifications.
+ </t>
+ </abstract>
+ </front>
+ <middle>
+ <section title="INTRODUCTION">
+ <t> Internet technical specifications often need to define a formal
+ syntax and are free to employ whatever notation their authors deem
+ useful. Over the years, a modified version of Backus-Naur Form
+ (BNF), called Augmented BNF (ABNF), has been popular among many
+ Internet specifications. It balances compactness and simplicity,
+ with reasonable representational power. In the early days of the
+ Arpanet, each specification contained its own definition of ABNF.
+ This included the email specifications, <xref target="RFC733"
+ ></xref> and then <xref target="RFC822"></xref>, which came to be the
+ common citations for defining ABNF. The current document separates those
+ definitions to permit selective reference. Predictably, it
+ also provides some modifications and enhancements.</t>
+ <t> The differences between standard BNF and ABNF involve naming rules,
+ repetition, alternatives, order-independence, and value ranges.
+ <xref target="CORE"></xref> supplies rule definitions and
+ encoding for a core lexical analyzer of the type common to several
+ Internet specifications. It is provided as a convenience and is
+ otherwise separate from the meta language defined in the body of
+ this document, and separate from its formal status. <list
+ style="hanging">
+ <t
+ hangText="Changes since [RFC2234]:"></t>
+ <t>In <xref target="SpecRep"></xref>, the phrase: "That is,
+ exactly <N> occurrences of
+ <element>." was corrected to: "That is, exactly
+ <n> occurrences of <element>."</t>
+ <t>Some continuation comment lines needed to be corrected to
+ begin with comment character (";").</t>
+ </list>
+ </t>
+ </section>
+ <section title="RULE DEFINITION">
+ <section title="Rule Naming">
+ <t> The name of a rule is simply the name itself; that is, a
+ sequence of characters, beginning with an alphabetic character,
+ and followed by a combination of alphabetics, digits, and hyphens
+ (dashes).</t>
+ <t>
+ <list style="hanging">
+ <t hangText="NOTE: "></t>
+ <t>Rule names are case-insensitive </t>
+ </list>
+ </t>
+ <t> The names <rulename>, <Rulename>,
+ <RULENAME>, and <rUlENamE> all refer
+ to the same rule.</t>
+ <t> Unlike original BNF, angle brackets ("<", ">") are
+ not required. However, angle brackets may be used around a rule
+ name whenever their presence facilitates in discerning the use
+ of a rule name. This is typically restricted to rule name
+ references in free-form prose, or to distinguish partial rules
+ that combine into a string not separated by white space, such as
+ shown in the discussion about repetition, below.</t>
+ </section>
+ <section title="Rule Form">
+ <t> A rule is defined by the following sequence:</t>
+ <figure>
+ <artwork type="example"><![CDATA[
+ name = elements crlf ]]></artwork>
+ </figure>
+ <t> 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
+ indicator (carriage return followed by line feed). The equal sign
+ separates the name from the definition of the rule. The elements
+ form a sequence of one or more rule names and/or value
+ definitions, combined according to the various operators defined
+ in this document, such as alternative and repetition.</t>
+ <t> For visual ease, rule definitions are left aligned. When a rule
+ requires multiple lines, the continuation lines are indented. 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.</t>
+ </section>
+ <section title="Terminal Values">
+ <t> Rules resolve into a string of terminal values, sometimes called
+ characters. In ABNF, a character is merely a non-negative integer.
+ In certain contexts, a specific mapping (encoding) of values into
+ a character set (such as ASCII) will be specified.</t>
+ <figure>
+ <preamble> Terminals are specified by one or more numeric
+ characters, with the base interpretation of those characters
+ indicated explicitly. The following bases are currently
+ defined:</preamble>
+ <artwork type="example"><![CDATA[
+ b = binary
+
+ d = decimal
+
+ x = hexadecimal ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> Hence:</preamble>
+ <artwork type="example"><![CDATA[
+ CR = %d13
+
+ CR = %x0D ]]></artwork>
+ <postamble> respectively specify the decimal and hexadecimal
+ representation of <xref target="US-ASCII"></xref> for carriage
+ return.</postamble>
+ </figure>
+ <figure>
+ <preamble> A concatenated string of such values is specified
+ compactly, using a period (".") to indicate a separation of
+ characters within that value. Hence:</preamble>
+ <artwork type="example"><![CDATA[
+ CRLF = %d13.10 ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> ABNF permits the specification of literal text strings directly,
+ enclosed in quotation-marks. Hence:</preamble>
+ <artwork type="example"><![CDATA[
+ command = "command string" ]]></artwork>
+ </figure>
+ <t> Literal text strings are interpreted as a concatenated set of
+ printable characters.</t>
+ <t>
+ <list style="hanging">
+ <t hangText="NOTE: "></t>
+ <t>ABNF strings are case-insensitive and the character set for
+ these strings is us-ascii. </t>
+ </list>
+ </t>
+ <figure>
+ <preamble> Hence:</preamble>
+ <artwork type="example"><![CDATA[
+ rulename = "abc" ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> and:</preamble>
+ <artwork type="example"><![CDATA[
+ rulename = "aBc"
+]]></artwork>
+ <postamble> will match "abc", "Abc", "aBc", "abC", "ABc", "aBC",
+ "AbC", and "ABC".</postamble>
+ </figure>
+ <t>
+ <list>
+ <t> To specify a rule that IS case SENSITIVE, specify the
+ characters individually. </t>
+ </list>
+ </t>
+ <figure>
+ <preamble> For example:</preamble>
+ <artwork type="example"><![CDATA[
+ rulename = %d97 %d98 %d99
+]]></artwork>
+ </figure>
+ <figure>
+ <preamble> or</preamble>
+ <artwork type="example"><![CDATA[
+ rulename = %d97.98.99
+]]></artwork>
+ <postamble> will match only the string that comprises only the
+ lowercased characters, abc.</postamble>
+ </figure>
+ </section>
+ <section title="External Encodings">
+ <t> External representations of terminal value characters will vary
+ according to constraints in the storage or transmission
+ environment. Hence, the same ABNF-based grammar may have multiple
+ external 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 Unicode is used. Encoding details are beyond the
+ scope of ABNF, although Appendix A (Core) provides definitions
+ for a 7-bit US-ASCII environment as has been common to much of
+ the Internet.</t>
+ <t> By separating external encoding from the syntax, it is intended
+ that alternate encoding environments can be used for the same
+ syntax.</t>
+ </section>
+ </section>
+ <section title="OPERATORS">
+ <section title="Concatenation: Rule1 Rule2">
+ <t> A rule can define a simple, ordered string of values (i.e., a
+ concatenation of contiguous characters) by listing a sequence
+ of rule names. For example:</t>
+ <figure>
+ <artwork type="example"><![CDATA[
+ foo = %x61 ; a
+
+ bar = %x62 ; b
+
+ mumble = foo bar foo ]]></artwork>
+ </figure>
+ <t>
+ So that the rule <mumble> matches the
+ lowercase string "aba".
+ </t>
+ <t>
+ LINEAR WHITE SPACE: Concatenation is at the core of the
+ ABNF parsing model. A string of contiguous characters
+ (values) is parsed according to the rules defined in ABNF.
+ For Internet specifications, there is some history of
+ permitting linear white space (space and horizontal tab) to
+ be freely and implicitly interspersed around major
+ constructs, such as delimiting special characters or atomic
+ strings.
+ </t>
+ <t>NOTE:
+ <list>
+ <t>
+ This specification for ABNF does not provide for
+ implicit specification of linear white space.</t>
+ </list>
+ </t>
+ <t> Any grammar that wishes to permit linear white space around
+ delimiters or string segments must specify it explicitly. It is
+ often useful to provide for such white space in "core" rules that
+ are then used variously among higher-level rules. The "core"
+ rules might be formed into a lexical analyzer or simply be part
+ of the main ruleset.</t>
+ </section>
+ <section anchor="Alternatives" title="Alternatives: Rule1 / Rule2">
+ <t> Elements separated by a forward slash ("/") are alternatives.
+ Therefore,</t>
+ <figure>
+ <artwork type="example"><![CDATA[
+ foo / bar
+]]></artwork>
+ <postamble> will accept <foo> or
+ <bar>.</postamble>
+ </figure>
+ <t>
+ <list style="hanging">
+ <t hangText="NOTE: "></t>
+ <t>A quoted string containing alphabetic characters is a special
+ form for specifying alternative characters and is
+ interpreted as a non-terminal representing the set of
+ combinatorial strings with the contained characters, in the
+ specified order but with any mixture of upper and lower
+ case.</t>
+ </list>
+ </t>
+ </section>
+ <section anchor="Incremental"
+ title="Incremental Alternatives: Rule1 =/ Rule2">
+ <t> It is sometimes convenient to specify a list of alternatives in
+ fragments. That is, an initial rule may match one or more
+ alternatives, with later rule definitions adding to the set of
+ alternatives. This is particularly useful for otherwise,
+ independent specifications that derive from the same parent rule
+ set, such as often occurs with parameter lists. ABNF permits this
+ incremental definition through the construct:</t>
+ <figure>
+ <artwork type="example"><![CDATA[
+ oldrule =/ additional-alternatives ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> So that the rule set</preamble>
+ <artwork type="example"><![CDATA[
+ ruleset = alt1 / alt2
+
+ ruleset =/ alt3
+
+ ruleset =/ alt4 / alt5 ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> is the same as specifying</preamble>
+ <artwork type="example"><![CDATA[
+ ruleset = alt1 / alt2 / alt3 / alt4 / alt5 ]]></artwork>
+ </figure>
+ </section>
+ <section anchor="Range" title="Value Range Alternatives: %c##-##">
+ <figure>
+ <preamble> A range of alternative numeric values can be specified
+ compactly, using dash ("-") to indicate the range of
+ alternative values. Hence:</preamble>
+ <artwork type="example"><![CDATA[
+ DIGIT = %x30-39 ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> is equivalent to:</preamble>
+ <artwork type="example"><![CDATA[
+ DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" /
+
+ "7" / "8" / "9" ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> Concatenated numeric values and numeric value ranges
+ cannot be specified in the same string. A numeric value may
+ use the dotted notation for concatenation or it may use the
+ dash notation to specify one value range. Hence, to specify
+ one printable character between end of line sequences, the
+ specification could be:</preamble>
+ <artwork type="example"><![CDATA[
+ char-line = %x0D.0A %x20-7E %x0D.0A ]]></artwork>
+ </figure>
+ </section>
+ <section anchor="Sequence" title="Sequence Group: (Rule1 Rule2)">
+ <figure>
+ <preamble> Elements enclosed in parentheses are treated as a
+ single element, whose contents are STRICTLY ORDERED. Thus,</preamble>
+ <artwork type="example"><![CDATA[
+ elem (foo / bar) blat
+]]></artwork>
+ <postamble>matches (elem foo blat) or (elem bar
+ blat), and</postamble>
+ </figure>
+ <figure>
+ <artwork type="example"><![CDATA[
+ elem foo / bar blat
+]]></artwork>
+ <postamble> matches (elem foo) or (bar blat).</postamble>
+ </figure>
+ <t>
+ <list style="hanging">
+ <t hangText="NOTE: "></t>
+ <t>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.
+ </t>
+ </list>
+ </t>
+ <figure>
+ <preamble> Hence, it is recommended that the following form be used:</preamble>
+ <artwork type="example"><![CDATA[
+ (elem foo) / (bar blat)
+]]></artwork>
+ <postamble>It will avoid misinterpretation by casual
+ readers.</postamble>
+ </figure>
+ <t> The sequence group notation is also used within free text to set
+ off an element sequence from the prose.</t>
+ </section>
+ <section anchor="VarRep" title="Variable Repetition: *Rule">
+ <figure>
+ <preamble> The operator "*" preceding an element indicates
+ repetition. The full form is:</preamble>
+ <artwork type="example"><![CDATA[
+ <a>*<b>element
+]]></artwork>
+ <postamble> where <a> and <b> are
+ optional decimal values, indicating at least <a>
+ and at most <b> occurrences of the
+ element.</postamble>
+ </figure>
+ <t> Default values are 0 and infinity so that
+ *<element> allows any number, including zero;
+ 1*<element> requires at least one;
+ 3*3<element> allows exactly 3 and
+ 1*2<element> allows one or two.</t>
+ </section>
+ <section anchor="SpecRep" title="Specific Repetition: nRule">
+ <figure>
+ <preamble> A rule of the form:</preamble>
+ <artwork type="example"><![CDATA[
+ <n>element ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> is equivalent to</preamble>
+ <artwork type="example"><![CDATA[
+ <n>*<n>element ]]></artwork>
+ </figure>
+ <t> That is, exactly <n> occurrences of
+ <element>. Thus, 2DIGIT is a 2-digit number, and
+ 3ALPHA is a string of three alphabetic characters.</t>
+ </section>
+ <section anchor="OptSeq" title="Optional Sequence: [RULE]">
+ <figure>
+ <preamble> Square brackets enclose an optional element sequence:</preamble>
+ <artwork type="example"><![CDATA[
+ [foo bar] ]]></artwork>
+ </figure>
+ <figure>
+ <preamble> is equivalent to</preamble>
+ <artwork type="example"><![CDATA[
+ *1(foo bar). ]]></artwork>
+ </figure>
+ </section>
+ <section anchor="Comment" title="Comment: ; Comment">
+ <t> 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 specifications.</t>
+ </section>
+ <section title="Operator Precedence">
+ <t> The various mechanisms described above have the following
+ precedence, from highest (binding tightest) at the top, to lowest
+ (loosest) at the bottom: <list>
+ <t>Strings, Names formation</t>
+ <t>Comment</t>
+ <t>Value range</t>
+ <t>Repetition</t>
+ <t>Grouping, Optional</t>
+ <t>Concatenation</t>
+ <t>Alternative</t>
+ </list>
+ </t>
+ <t> Use of the alternative operator, freely mixed with
+ concatenations, can be confusing.</t>
+ <t>
+ <list>
+ <t> Again, it is recommended that the grouping operator be
+ used to make explicit concatenation groups. </t>
+ </list>
+ </t>
+ </section>
+ </section>
+ <section title="ABNF DEFINITION OF ABNF">
+ <t>
+ <list style="hanging">
+ <t hangText="NOTES:">
+ <list style="numbers">
+ <t>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.</t>
+ <t>This syntax uses the rules provided in <xref
+ target="CORE"></xref> (Core).</t>
+ </list>
+ </t>
+ </list>
+ </t>
+ <figure>
+ <artwork type="abnf"><![CDATA[
+ rulelist = 1*( rule / (*c-wsp c-nl) )
+
+ rule = rulename defined-as elements c-nl
+ ; continues if next line starts
+ ; with white space
+
+ rulename = ALPHA *(ALPHA / DIGIT / "-")
+
+ defined-as = *c-wsp ("=" / "=/") *c-wsp
+ ; basic rules definition and
+ ; incremental alternatives
+
+ elements = alternation *c-wsp
+
+ c-wsp = WSP / (c-nl WSP)
+
+ c-nl = comment / CRLF
+ ; comment or newline
+
+ comment = ";" *(WSP / VCHAR) CRLF
+
+ alternation = concatenation
+ *(*c-wsp "/" *c-wsp concatenation)
+
+ concatenation = repetition *(1*c-wsp repetition)
+
+ repetition = [repeat] element
+
+ repeat = 1*DIGIT / (*DIGIT "*" *DIGIT)
+
+ element = rulename / group / option /
+ char-val / num-val / prose-val
+
+ group = "(" *c-wsp alternation *c-wsp ")"
+
+ option = "[" *c-wsp alternation *c-wsp "]"
+
+ char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
+ ; quoted string of SP and VCHAR
+ ; without DQUOTE
+
+ num-val = "%" (bin-val / dec-val / hex-val)
+
+ bin-val = "b" 1*BIT
+ [ 1*("." 1*BIT) / ("-" 1*BIT) ]
+ ; series of concatenated bit values
+ ; or single ONEOF range
+
+ dec-val = "d" 1*DIGIT
+ [ 1*("." 1*DIGIT) / ("-" 1*DIGIT) ]
+
+ hex-val = "x" 1*HEXDIG
+ [ 1*("." 1*HEXDIG) / ("-" 1*HEXDIG) ]
+
+ prose-val = "<" *(%x20-3D / %x3F-7E) ">"
+ ; bracketed string of SP and VCHAR
+ ; without angles
+ ; prose description, to be used as
+ ; last resort ]]>
+</artwork>
+ </figure>
+ </section>
+ <section title="SECURITY CONSIDERATIONS">
+ <t> Security is truly believed to be irrelevant to this document.</t>
+ </section>
+ </middle>
+ <back>
+ <references title="Normative References">
+ <reference anchor="US-ASCII">
+ <front>
+ <title>Coded Character Set -- 7-bit American Standard Code for
+ Information Interchange</title>
+ <author>
+ <organization>American National Standards
+ Institute</organization>
+ </author>
+ <date year="1986"></date>
+ </front>
+ <seriesInfo name="ANSI" value="X3.4"></seriesInfo>
+ </reference>
+ </references>
+ <references title="Informative References">
+ <reference anchor="RFC733">
+ <front>
+ <title>Standard for the format of ARPA network text messages</title>
+ <author fullname="David H. Crocker" initials="D."
+ surname="Crocker">
+ <organization>The Rand Corporation, Information Sciences
+ Department</organization>
+ <address>
+ <postal>
+ <street>1700 Main St</street>
+ <city>Santa Monica</city>
+ <region>CA</region>
+ <code>90406</code>
+ <country>US</country>
+ </postal>
+ <email>DCrocker@Rand-Unix</email>
+ </address>
+ </author>
+ <author fullname="John J. Vittal" initials="J." surname="Vittal">
+ <organization>Bolt Beranek and Newman Inc. (BBN)</organization>
+ <address>
+ <postal>
+ <street>50 Moulton St.</street>
+ <city>Cambridge</city>
+ <region>MA</region>
+ <code>02138</code>
+ <country>US</country>
+ </postal>
+ <email>Vittal@BBN-TenexD</email>
+ </address>
+ </author>
+ <author fullname="Kenneth T. Pogran" initials="K."
+ surname="Pogran">
+ <organization>Massachusets Institute of Technology (MIT),
+ Laboratory for Computer Science</organization>
+ <address>
+ <postal>
+ <street>545 Technology Square</street>
+ <city>Cambridge</city>
+ <region>MA</region>
+ <code>02139</code>
+ <country>US</country>
+ </postal>
+ <email>Pogran@MIT-Multics</email>
+ </address>
+ </author>
+ <author fullname="D. Austin Henderson, Jr." initials="D."
+ surname="Henderson">
+ <organization>Bolt Beranek and Newman Inc. (BBN)</organization>
+ <address>
+ <postal>
+ <street>50 Moulton St.</street>
+ <city>Cambridge</city>
+ <region>MA</region>
+ <code>02138</code>
+ <country>US</country>
+ </postal>
+ <email>Henderson@BBN-TenexD</email>
+ </address>
+ </author>
+ <date day="21" month="November" year="1977"></date>
+ </front>
+ <seriesInfo name="RFC" value="733"></seriesInfo>
+ </reference>
+ <reference anchor="RFC822">
+ <front>
+ <title abbrev="Standard for ARPA Internet Text Messages">Standard
+ for the format of ARPA Internet text messages</title>
+ <author fullname="David H. Crocker" initials="D.H."
+ surname="Crocker">
+ <organization>University of Delaware, Dept. of Electrical
+ Engineering</organization>
+ <address>
+ <postal>
+ <street></street>
+ <city>Newark</city>
+ <region>DE</region>
+ <code>19711</code>
+ <country>US</country>
+ </postal>
+ <email>DCrocker@UDel-Relay</email>
+ </address>
+ </author>
+ <date day="13" month="August" year="1982"></date>
+ </front>
+ <seriesInfo name="STD" value="11"></seriesInfo>
+ <seriesInfo name="RFC" value="822"></seriesInfo>
+ </reference>
+ <reference anchor="RFC2234">
+ <front>
+ <title>Augmented BNF for Syntax Specifications: ABNF</title>
+ <author fullname="Dave Crocker" initials="D." surname="Crocker">
+ <organization>Internet Mail Consortium</organization>
+ </author>
+ <author fullname="Paul Overell" initials="P." surname="Overell">
+ <organization>Demon Internet Ltd.</organization>
+ </author>
+ <date month="November" year="1997"></date>
+ </front>
+ <seriesInfo name="RFC" value="2234"></seriesInfo>
+ </reference>
+ </references>
+ <section title="ACKNOWLEDGEMENTS">
+ <t> 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.</t>
+ <t> 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.</t>
+ <t> 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.</t>
+ <t>Julian Reschke warrants a special thanks for converting the Draft
+ Standard version to XML source form.</t>
+ </section>
+ <section anchor="CORE" title="APPENDIX - CORE ABNF OF ABNF">
+ <t> This Appendix is provided as a convenient core for specific
+ grammars. The definitions may be used as a core set of rules.</t>
+ <section title="Core Rules">
+ <t> Certain basic rules are in uppercase, such as SP, HTAB, CRLF,
+ DIGIT, ALPHA, etc.</t>
+ <figure>
+ <artwork type="abnf"><![CDATA[
+ ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
+
+ BIT = "0" / "1"
+
+ CHAR = %x01-7F
+ ; any 7-bit US-ASCII character,
+ ; excluding NUL
+
+ CR = %x0D
+ ; carriage return
+
+ CRLF = CR LF
+ ; Internet standard newline
+
+ CTL = %x00-1F / %x7F
+ ; controls
+
+ DIGIT = %x30-39
+ ; 0-9
+
+ DQUOTE = %x22
+ ; " (Double Quote)
+
+ HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
+
+ HTAB = %x09
+ ; horizontal tab
+
+ LF = %x0A
+ ; linefeed
+
+ LWSP = *(WSP / CRLF WSP)
+ ; linear white space (past newline)
+
+ OCTET = %x00-FF
+ ; 8 bits of data
+
+ SP = %x20
+
+ VCHAR = %x21-7E
+ ; visible (printing) characters
+
+ WSP = SP / HTAB
+ ; white space ]]>
+</artwork>
+ </figure>
+ </section>
+ <section title="Common Encoding">
+ <t> 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 zero. A string of values is in "network byte order", in which
+ the higher-valued bytes are represented on the left-hand side and
+ are sent over the network first.</t>
+ </section>
+ </section>
+ </back>
+</rfc>
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