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Augmented Backus-Naur Form (ABNF) Notation and Rules
RFC 5234

 

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|   Core rules   |   Operators   |   Definition   |


Concatenation
Rule1   Rule2
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Alternatives
Rule1  /  Rule2
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Incremental Alternatives
Rule1  =/  Rule2
The rule set:
ruleset = alt1 / alt2
ruleset /= alt3
is the same as specifying:
ruleset = alt1 / alt2 / alt3
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Value Range Alternatives
%c##-##
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Sequence Group
Rule1   Rule2 )
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Variable Repetition
*Rule
The full form is: <a>*<b>element
where <a> and <b> are optional decimal values,
indicating at least <a> and at most <b> occurrences of element.
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
1*2<element>
allows one or two
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Specific Repetition
nRule
A rule of the form: <n>element
is equivalent to: <n>*<n>element
That is, exactly <n> occurrences of <element>.
Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters.
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Optional Sequence
Rule ]
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Comment
;  Comment
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