108:
943:
1491:
Use of this linear-white-space rule permits lines containing only white space that are no longer legal in mail headers and have caused interoperability problems in other contexts. Do not use when defining mail headers and use with caution in other
257:
White space is used to separate elements of a definition; for space to be recognized as a delimiter, it must be explicitly included. The explicit reference for a single whitespace character is
236:
will only match "aBc". Prior to that, a case-sensitive string could only be specified by listing the individual characters: to match “aBc”, the definition would be
1615:
934:
Use of the alternative operator with concatenation may be confusing, and it is recommended that grouping be used to make explicit concatenation groups.
175:) are not required around rule names (as they are in BNF). However, they may be used to delimit a rule name when used in prose to discern a rule name.
145:, the definition consists of sequences of symbols that define the rule, a comment for documentation, and ending with a carriage return and line feed.
1666:
1608:
269:
definition in RFC5234 is controversial because at least one whitespace character is needed to form a delimiter between two fields.
272:
Definitions are left-aligned. When multiple lines are required (for readability), continuation lines are indented by whitespace.
1651:
232:
will match “abc”, “Abc”, “aBc”, “abC”, “ABc”, “AbC”, “aBC”, and “ABC”. RFC 7405 added a syntax for case-sensitive strings:
1601:
1564:
1661:
1514:
1172:
The (U.S.) postal address example given in the augmented Backus–Naur form (ABNF) page may be specified as follows:
1697:
39:(BNF), but consisting of its own syntax and derivation rules. The motive principle for ABNF is to describe a
1646:
107:
44:
1702:
1676:
372:
1641:
228:). These strings are case-insensitive, and the character set used is (US-)ASCII. Therefore, the string
36:
164:
all refer to the same rule. Rule names consist of a letter followed by letters, numbers, and hyphens.
1584:
782:
217:
in hexadecimal. A carriage return followed by a line feed may be specified with concatenation as
908:
The following operators have the given precedence from tightest binding to loosest binding:
139:
92:
76:
68:
54:
20:
758:
gives the minimal number of elements to be included (with the default of 0). The optional
183:
947:
112:
1691:
40:
762:
gives the maximal number of elements to be included (with the default of infinity).
1536:
224:
Literal text is specified through the use of a string enclosed in quotation marks (
32:
205:= hexadecimal), followed by the value, or concatenation of values (indicated by
142:
96:
84:
80:
72:
58:
88:
1624:
942:
1164:
in the RFC spec. They are named here for clarity in the main syntax diagram.
856:
To indicate an optional element, the following constructions are equivalent:
1560:
99:
updates it, adding a syntax for specifying case-sensitive string literals.
1510:
539:
A range of numeric values may be specified through the use of a hyphen (
1593:
265:
is for zero or more whitespace characters with newlines permitted. The
240:. A string can also be explicitly specified as case-insensitive with a
1484:
637:
To match "a b d" or "a c d", the following rule could be constructed:
634:
Elements may be placed in parentheses to group rules in a definition.
1487:
adds a warning in conjunction to the definition of LWSP as follows:
371:
A rule may be defined by a list of alternative rules separated by a
48:
673:
To match “a b” or “c d”, the following rules could be constructed:
1671:
941:
424:
Additional alternatives may be added to a rule through the use of
106:
1656:
62:
1597:
119:
An ABNF specification is a set of derivation rules, written as
305:
To match the string “aba”, the following rules could be used:
53:("STD 68", type case sic), which as of December 2010 is
302:
A rule may be defined by listing a sequence of rule names.
289:) starts a comment that continues to the end of the line.
189:
Numeric characters may be specified as the percent sign
813:
To indicate an explicit number of elements, the form
61:, and it often serves as the definition language for
883:
864:
860:
702:
677:
641:
568:
550:
491:
467:
454:
435:
394:
341:
325:
309:
209:). For example, a carriage return is specified by
954:The core rules are defined in the ABNF standard.
186:are specified by one or more numeric characters.
1537:"Augmented BNF for Syntax Specifications: ABNF"
1489:
977:Upper- and lower-case ASCII letters (A–Z, a–z)
750:To indicate repetition of an element, the form
1609:
8:
43:of a language to be used as a bidirectional
16:Metalanguage based on Backus–Naur Form (BNF)
390:, the following rule could be constructed:
1616:
1602:
1594:
428:between the rule name and the definition.
1535:Crocker, D.; Overell, P. (January 2008).
996:DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
1148:Note that in the core rules diagram the
956:
1502:
1511:"Official Internet Protocol Standards"
7:
1567:from the original on 9 February 2010
1517:from the original on 9 February 2010
1076:Any ASCII character, excluding NUL
999:Hexadecimal digits (0–9, A–F, a-f)
1054:Linear white space (past newline)
14:
148:Rule names are case-insensitive:
837:
828:to get two numeric digits, and
781:for two or three elements, cf.
1065:Visible (printing) characters
832:to get three numeric digits. (
777:for one or more elements, and
1:
817:is used and is equivalent to
487:is therefore equivalent to
1662:Syntax Definition Formalism
769:for zero or more elements,
1719:
1563:. RFC Editor. 2010-02-19.
1513:. RFC Editor. 2010-02-21.
1131:Internet-standard newline
819:<a>*<a>element
752:<a>*<b>element
261:(linear white space), and
25:augmented Backus–Naur form
1632:
1043:Space and horizontal tab
773:for zero or one element,
65:communication protocols.
1542:. RFC Editor. p. 16
1174:
912:Strings, names formation
836:is defined below under "
415:Incremental alternatives
193:, followed by the base (
121:
1647:Definite clause grammar
844:in the example below.)
45:communications protocol
1494:
1152:charset is inlined in
951:
754:is used. The optional
116:
1677:Wirth syntax notation
988:Decimal digits (0–9)
945:
110:
50:Internet Standard 68
904:Operator precedence
804:Specific repetition
783:regular expressions
741:Variable repetition
382:To accept the rule
47:. It is defined by
952:
924:Grouping, optional
117:
1685:
1684:
1146:
1145:
1051:*(WSP / CRLF WSP)
974:%x41–5A / %x61–7A
963:Formal definition
848:Optional sequence
564:is equivalent to
1710:
1698:Formal languages
1642:Backus–Naur form
1618:
1611:
1604:
1595:
1588:
1582:
1576:
1575:
1573:
1572:
1557:
1551:
1550:
1548:
1547:
1541:
1532:
1526:
1525:
1523:
1522:
1507:
1475:
1472:
1469:
1466:
1463:
1460:
1457:
1454:
1451:
1448:
1445:
1442:
1439:
1436:
1433:
1430:
1427:
1424:
1421:
1418:
1415:
1412:
1409:
1406:
1403:
1400:
1397:
1394:
1391:
1388:
1385:
1382:
1379:
1376:
1373:
1370:
1367:
1364:
1361:
1358:
1355:
1352:
1349:
1346:
1343:
1340:
1337:
1334:
1331:
1328:
1325:
1322:
1319:
1316:
1313:
1310:
1307:
1304:
1301:
1298:
1295:
1292:
1289:
1286:
1283:
1280:
1277:
1274:
1271:
1268:
1265:
1262:
1259:
1256:
1253:
1250:
1247:
1244:
1241:
1238:
1235:
1232:
1229:
1226:
1223:
1220:
1217:
1214:
1211:
1208:
1205:
1202:
1199:
1196:
1193:
1190:
1187:
1184:
1181:
1178:
1109:Carriage return
957:
899:
898:
895:
892:
889:
886:
880:
879:
876:
873:
870:
867:
861:
853:
835:
831:
827:
820:
816:
815:<a>element
810:
799:
795:
791:
787:
780:
776:
772:
768:
761:
757:
753:
747:
736:
735:
732:
729:
726:
723:
720:
717:
714:
711:
708:
705:
699:
698:
695:
692:
689:
686:
683:
680:
669:
668:
665:
662:
659:
656:
653:
650:
647:
644:
631:
620:
619:
616:
613:
610:
607:
604:
601:
598:
595:
592:
589:
586:
583:
580:
577:
574:
571:
560:
559:
556:
553:
542:
536:
525:
524:
521:
518:
515:
512:
509:
506:
503:
500:
497:
494:
483:
482:
479:
476:
473:
470:
464:
463:
460:
457:
451:
450:
447:
444:
441:
438:
427:
421:
410:
409:
406:
403:
400:
397:
378:
368:
357:
356:
353:
350:
347:
344:
338:
337:
334:
331:
328:
322:
321:
318:
315:
312:
299:
288:
282:
268:
264:
260:
243:
239:
235:
231:
227:
220:
216:
212:
208:
204:
200:
196:
192:
174:
170:
167:Angle brackets (
163:
162:<rUlENamE>
159:
158:<RULENAME>
155:
154:<Rulename>
151:
150:<rulename>
140:case-insensitive
138:where rule is a
134:
131:
128:
125:
37:Backus–Naur form
21:computer science
1718:
1717:
1713:
1712:
1711:
1709:
1708:
1707:
1688:
1687:
1686:
1681:
1628:
1622:
1592:
1591:
1585:RFC Errata 3096
1583:
1579:
1570:
1568:
1559:
1558:
1554:
1545:
1543:
1539:
1534:
1533:
1529:
1520:
1518:
1509:
1508:
1504:
1499:
1482:
1477:
1476:
1473:
1470:
1467:
1464:
1461:
1458:
1455:
1452:
1449:
1446:
1443:
1440:
1437:
1434:
1431:
1428:
1425:
1422:
1419:
1416:
1413:
1410:
1407:
1404:
1401:
1398:
1395:
1392:
1389:
1386:
1383:
1380:
1377:
1374:
1371:
1368:
1365:
1362:
1359:
1356:
1353:
1350:
1347:
1344:
1341:
1338:
1335:
1332:
1329:
1326:
1323:
1320:
1317:
1314:
1311:
1308:
1305:
1303:"Sr."
1302:
1299:
1297:"Jr."
1296:
1293:
1290:
1287:
1284:
1281:
1278:
1275:
1272:
1269:
1266:
1263:
1260:
1257:
1254:
1251:
1248:
1245:
1242:
1239:
1236:
1233:
1230:
1227:
1224:
1221:
1218:
1215:
1212:
1209:
1206:
1203:
1200:
1197:
1194:
1191:
1188:
1185:
1182:
1179:
1176:
1170:
1087:8 bits of data
1032:Horizontal tab
940:
906:
896:
893:
890:
887:
884:
877:
874:
871:
868:
865:
852:
850:
833:
829:
825:
818:
814:
808:
806:
797:
793:
789:
785:
778:
774:
770:
766:
759:
755:
751:
745:
743:
733:
730:
727:
724:
721:
718:
715:
712:
709:
706:
703:
696:
693:
690:
687:
684:
681:
678:
666:
663:
660:
657:
654:
651:
648:
645:
642:
629:
627:
617:
614:
611:
608:
605:
602:
599:
596:
593:
590:
587:
584:
581:
578:
575:
572:
569:
557:
554:
551:
540:
534:
532:
522:
519:
516:
513:
510:
507:
504:
501:
498:
495:
492:
480:
477:
474:
471:
468:
461:
458:
455:
448:
445:
442:
439:
436:
425:
419:
417:
407:
404:
401:
398:
395:
376:
366:
364:
354:
351:
348:
345:
342:
335:
332:
329:
326:
319:
316:
313:
310:
297:
295:
286:
280:
278:
266:
262:
258:
255:
250:
241:
237:
233:
229:
225:
218:
214:
210:
206:
202:
201:= decimal, and
198:
194:
190:
181:
179:Terminal values
172:
168:
161:
157:
153:
149:
136:
135:
133:; comment CR LF
132:
129:
126:
123:
105:
17:
12:
11:
5:
1716:
1714:
1706:
1705:
1700:
1690:
1689:
1683:
1682:
1680:
1679:
1674:
1669:
1664:
1659:
1654:
1649:
1644:
1639:
1633:
1630:
1629:
1623:
1621:
1620:
1613:
1606:
1598:
1590:
1589:
1577:
1552:
1527:
1501:
1500:
1498:
1495:
1481:
1478:
1177:postal-address
1175:
1169:
1166:
1160:is inlined in
1144:
1143:
1140:
1137:
1133:
1132:
1129:
1126:
1122:
1121:
1118:
1115:
1111:
1110:
1107:
1104:
1100:
1099:
1096:
1095:%x00–1F / %x7F
1093:
1089:
1088:
1085:
1082:
1078:
1077:
1074:
1071:
1067:
1066:
1063:
1060:
1056:
1055:
1052:
1049:
1045:
1044:
1041:
1038:
1034:
1033:
1030:
1027:
1023:
1022:
1019:
1016:
1012:
1011:
1008:
1005:
1001:
1000:
997:
994:
990:
989:
986:
983:
979:
978:
975:
972:
968:
967:
964:
961:
948:syntax diagram
939:
936:
932:
931:
928:
925:
922:
919:
916:
913:
905:
902:
901:
900:
881:
862:
849:
846:
805:
802:
742:
739:
738:
737:
700:
671:
670:
626:
625:Sequence group
623:
622:
621:
562:
561:
531:
528:
527:
526:
485:
484:
465:
452:
420:Rule1 =/ Rule2
416:
413:
412:
411:
363:
360:
359:
358:
339:
323:
294:
291:
277:
274:
254:
251:
249:
246:
213:in decimal or
180:
177:
122:
113:syntax diagram
104:
101:
15:
13:
10:
9:
6:
4:
3:
2:
1715:
1704:
1703:Metalanguages
1701:
1699:
1696:
1695:
1693:
1678:
1675:
1673:
1670:
1668:
1665:
1663:
1660:
1658:
1655:
1653:
1650:
1648:
1645:
1643:
1640:
1638:
1635:
1634:
1631:
1626:
1619:
1614:
1612:
1607:
1605:
1600:
1599:
1596:
1586:
1581:
1578:
1566:
1562:
1556:
1553:
1538:
1531:
1528:
1516:
1512:
1506:
1503:
1496:
1493:
1488:
1486:
1479:
1408:","
1327:"X"
1321:"V"
1315:"I"
1249:"."
1231:personal-part
1225:personal-part
1204:personal-part
1173:
1167:
1165:
1163:
1159:
1155:
1151:
1142:Binary digit
1141:
1138:
1135:
1134:
1130:
1127:
1124:
1123:
1119:
1116:
1113:
1112:
1108:
1105:
1102:
1101:
1097:
1094:
1091:
1090:
1086:
1083:
1080:
1079:
1075:
1072:
1069:
1068:
1064:
1061:
1058:
1057:
1053:
1050:
1047:
1046:
1042:
1039:
1036:
1035:
1031:
1028:
1025:
1024:
1020:
1017:
1014:
1013:
1010:Double quote
1009:
1006:
1003:
1002:
998:
995:
992:
991:
987:
984:
981:
980:
976:
973:
970:
969:
965:
962:
959:
958:
955:
950:of core rules
949:
944:
937:
935:
929:
927:Concatenation
926:
923:
920:
917:
914:
911:
910:
909:
903:
882:
863:
859:
858:
857:
854:
847:
845:
843:
839:
822:
811:
803:
801:
784:
763:
748:
740:
701:
676:
675:
674:
640:
639:
638:
635:
632:
630:(Rule1 Rule2)
624:
618:"7"
612:"6"
606:"5"
600:"4"
594:"3"
588:"2"
582:"1"
576:"0"
567:
566:
565:
549:
548:
547:
544:
537:
529:
490:
489:
488:
466:
453:
434:
433:
432:
429:
422:
414:
393:
392:
391:
389:
385:
380:
374:
369:
367:Rule1 / Rule2
361:
340:
324:
308:
307:
306:
303:
300:
293:Concatenation
292:
290:
285:A semicolon (
283:
275:
273:
270:
252:
247:
245:
222:
187:
185:
178:
176:
165:
146:
144:
141:
120:
115:of ABNF rules
114:
109:
102:
100:
98:
94:
90:
86:
82:
78:
74:
70:
66:
64:
60:
56:
52:
51:
46:
42:
41:formal system
38:
34:
30:
26:
22:
1636:
1580:
1569:. Retrieved
1555:
1544:. Retrieved
1540:(plain text)
1530:
1519:. Retrieved
1505:
1490:
1483:
1171:
1161:
1157:
1153:
1149:
1147:
953:
933:
907:
855:
851:
841:
840:". Also see
823:
812:
807:
764:
749:
744:
672:
636:
633:
628:
563:
545:
538:
533:
486:
430:
423:
418:
387:
386:or the rule
383:
381:
370:
365:
304:
301:
296:
284:
279:
271:
256:
223:
188:
182:
166:
147:
137:
118:
67:
49:
33:metalanguage
28:
24:
18:
1561:"RFC Index"
1387:street-name
1345:street-name
930:Alternative
918:Value range
530:Value range
362:Alternative
298:Rule1 Rule2
253:White space
143:nonterminal
75:supersedes
1692:Categories
1625:Metasyntax
1571:2010-02-21
1546:2010-02-21
1521:2010-02-21
1497:References
1255:first-name
1237:first-name
938:Core rules
921:Repetition
838:Core rules
779:2*3element
238:%d97.66.99
197:= binary,
130:definition
1627:notations
1492:contexts.
1429:town-name
1405:town-name
1363:house-num
1339:house-num
1276:last-name
1219:name-part
1213:last-name
1192:name-part
1183:name-part
1162:prose-val
1139:"0" / "1"
1120:Linefeed
1098:Controls
1040:SP / HTAB
775:1*element
771:*1element
760:<b>
756:<a>
546:The rule
431:The rule
281:; comment
248:Operators
184:Terminals
35:based on
1565:Archived
1515:Archived
1485:RFC 5234
1480:Pitfalls
1465:zip-code
1423:zip-code
1399:zip-part
1189:zip-part
1154:char-val
966:Meaning
842:zip-code
767:*element
244:prefix.
103:Overview
1267:initial
1246:initial
1168:Example
1084:%x00–FF
1073:%x01–7F
1062:%x21–7E
985:%x30–39
915:Comment
746:n*nRule
558:%x30-37
535:%c##-##
493:ruleset
469:ruleset
456:ruleset
437:ruleset
373:solidus
276:Comment
234:%s"aBc"
219:%d13.10
31:) is a
1333:street
1288:suffix
1186:street
1021:Space
1004:DQUOTE
993:HEXDIG
830:3DIGIT
826:2DIGIT
798:e{2,3}
343:mumble
160:, and
95:
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1672:OMeta
1474:DIGIT
1462:ALPHA
1453:state
1441:ALPHA
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1396:VCHAR
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1375:DIGIT
1360:DIGIT
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1273:ALPHA
1264:ALPHA
1158:CHAR3
1150:CHAR2
1128:CR LF
1081:OCTET
1059:VCHAR
982:DIGIT
971:ALPHA
946:ABNF
894:snafu
891:fubar
875:snafu
872:fubar
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809:nRule
704:group
679:group
643:group
570:OCTAL
552:OCTAL
396:fubar
230:"abc"
111:ABNF
1667:TBNF
1657:JSGF
1652:EBNF
1637:ABNF
1426:CRLF
1348:CRLF
1228:CRLF
1216:CRLF
1156:and
1125:CRLF
1117:%x0A
1106:%x0D
1070:CHAR
1048:LWSP
1029:%x09
1026:HTAB
1018:%x20
1007:%x22
960:Rule
824:Use
796:and
765:Use
523:alt5
517:alt4
511:alt3
505:alt2
499:alt1
481:alt5
475:alt4
462:alt3
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333:%x62
317:%x61
267:LWSP
263:LWSP
215:%x0D
211:%d13
173:>
169:<
124:rule
97:7405
87:and
85:2234
81:4234
73:5234
63:IETF
59:5234
29:ABNF
1417:1*2
1369:1*8
1357:1*4
1351:apt
1136:BIT
1092:CTL
1037:WSP
885:0*1
543:).
408:bar
388:bar
379:).
352:bar
336:; b
327:bar
320:; a
259:WSP
93:RFC
89:733
77:RFC
69:RFC
55:RFC
19:In
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1447:SP
1435:1*
1420:SP
1411:SP
1393:1*
1342:SP
1330:))
1309:1*
1222:=/
1207:SP
1114:LF
1103:CR
1015:SP
866:*1
821:.
800:.
794:e+
792:,
790:e?
788:,
786:e*
472:=/
459:=/
426:=/
402:fu
384:fu
355:fu
349:fu
311:fu
242:%i
221:.
171:,
156:,
152:,
91:.
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23:,
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1603:v
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1471:5
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731:d
728:c
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722:/
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716:b
713:a
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585:/
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573:=
555:=
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287:;
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203:x
199:d
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