EBNF实例讲解（翻译自Extended BNF. ISO/IEC 14977 : 1996(E)）

实在是资料太少了，这作业写得我要死了。
资料都是英文的，我觉得直接看例子比较容易懂。
话不多说上例子了。

4.22 Further examples

The following example is a syntax-rule that states that a Fortran 77 continuation line starts with 5 blanks, the sixth character must not be a blank or zero, and there must not be more than 72 (= 5+1+66) characters altogether.

Fortran 77 continuation line=5*" “, (character - (” " | “0”)), 66 * [character] ;

In Fortran 66, the definition of a continuation line is more complicated. The following example is a syntax-rule that states that a continuation line must not start with C, there must be at least 6 characters, the sixth character must not be a blank or zero, and there must not be more than 72 (= 1+4+1+66) characters altogether.

Fortran 66 continuation line = character - “C”, 4 * character, character - (" " | “0”),
66 * [character] ;
下面的例子是一个语法规则，规定Fortran 77的延续行以5个空行开始，第6个字符不能是空行或0，并且总共不能超过72个字符（=5+1+66）。
Fortran 77延续行=5" “, (字符 - (” " | “0”)), 66 * [字符] ;
在Fortran 66中，延续行的定义比较复杂。下面的例子是一个语法规则，它规定了一个延续行不能以C开头，至少有6个字符，第六个字符不能是空的或0，而且总共不能超过72个字符(=1+4+1+66)。
Fortran 66延续行=字符-“C”，4*字符，字符-(" " | “0”)。
66 * [字符] 。*
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As examples the following syntax-rules illustrate the facilities for expressing repetition.

aa = “A”;
bb=3* aa, “B”; cc=3* [aa], “C”;
dd = {aa}, “D”;
ee = aa, {aa}, “E”;
ff=3* aa,3* [aa], “F”;
gg=3* {aa}, “D”;

Terminal-strings defined by these rules are as follows:

aa: A bb: AAAB
cc: C AC AAC AAAC
dd: D AD AAD AAAD AAAAD etc.
ee: AE AAE AAAE AAAAE AAAAAE etc. ff: AAAF AAAAF AAAAAF AAAAAAF

NOTE — The definition for gg, although syntactically valid, is not sensible. The sequences of symbols represented by gg are identical with those given by dd but cannot be parsed unambiguously.
这部分比较容易，不翻译了。
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As examples the following syntax-rules illustrate the facilities provided by the except-symbol.

letter = “A” | “B” | “C” | “D” | “E” | “F”
| “G” | “H” | “I” | “J” | “K” | “L” | “M”
| “N” | “O” | “P” | “Q” | “R” | “S” | “T”
| “U” | “V” | “W” | “X” | “Y” | “Z”;
vowel = “A” | “E” | “I” | “O” | “U”; consonant = letter - vowel;
ee = {“A”}-, “E”;

Terminal-strings defined by these rules are as follows:

letter: A B C D E F G H I J etc. vowel: A E I O U
consonant: B C D F G H J K L M etc. ee: AE AAE AAAE AAAAE AAAAAE etc.

NOTE — “A” - represents a sequence of one or more A’s because it is a syntactic-term with an empty syntactic-exception.

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串联符号	,
定义符号	=
定义分隔符（我理解类似于或）	竖线
结束评论符	*)
结束元组符号	)
结束选择符号	]
结束重复符号	}
集合差集符号	-
引用符号	·
重复符号	*
不理解
不理解
开始评论符号	(*
开始元组符号	(
开始选择符号	[
开始重复符号	{
终结符号	;

附上维基百科及翻译
可以省略或重复的表达式可以用大括号{…}表示：

自然数= 不包括零的数字， { digit } ；
在这种情况下，串1，2，…，10，…，10000，…都是正确的表达式。为了表示这一点，花括号中设置的所有内容都可以任意重复，包括根本不重复。

可以通过方括号[…]表示选项。也就是说，方括号内设置的所有内容可能只出现一次，或者根本不出现：

整数= “ 0” | [ “-” ]， 自然数；
因此，整数是零（0）或自然数，其后可以是可选的减号。

EBNF还提供（除其他外）语法，用于描述（指定次数）重复，排除生成的某些部分以及在EBNF语法中插入注释。

维基百科的其它例子（都是字面含义很容易懂）:
digit excluding zero = “1” | “2” | “3” | “4” | “5” | “6” | “7” | “8” | “9” ;
digit = “0” | digit excluding zero ;

twelve = “1”, “2” ;
two hundred one = “2”, “0”, “1” ;
three hundred twelve = “3”, twelve ;
twelve thousand two hundred one = twelve, two hundred one ;

letter = “A” | “B” | “C” | “D” | “E” | “F” | “G”
| “H” | “I” | “J” | “K” | “L” | “M” | “N”
| “O” | “P” | “Q” | “R” | “S” | “T” | “U”
| “V” | “W” | “X” | “Y” | “Z” | “a” | “b”
| “c” | “d” | “e” | “f” | “g” | “h” | “i”
| “j” | “k” | “l” | “m” | “n” | “o” | “p”
| “q” | “r” | “s” | “t” | “u” | “v” | “w”
| “x” | “y” | “z” ;
digit = “0” | “1” | “2” | “3” | “4” | “5” | “6” | “7” | “8” | “9” ;
symbol = “[” | “]” | “{” | “}” | “(” | “)” | “<” | “>”
| “’” | ‘"’ | “=” | “|” | “.” | “,” | “;” ;
character = letter | digit | symbol | “_” ;

identifier = letter , { letter | digit | “_” } ;
terminal = “’” , character , { character } , “’”
| ‘"’ , character , { character } , ‘"’ ;

lhs = identifier ;
rhs = identifier
| terminal
| “[” , rhs , “]”
| “{” , rhs , “}”
| “(” , rhs , “)”
| rhs , “|” , rhs
| rhs , “,” , rhs ;

rule = lhs , “=” , rhs , “;” ;
grammar = { rule } ;