" | Quotation marks are used to indicate that a
character that is normally part of the BNF syntax is used as a literal
character in the definition. The definition B"+"C,
for example, can only be replaced by the pattern B+C.
The definition B+C can be replaced by, for example,
patterns BC, BBC, or BBBC. |
A ::= B | Defines A as B.
For example, A::= B"+" | C means that A is
equivalent to either B+ or C.
The ::= notation is used to define a higher level
construct in terms of its components. Each component might also
have a ::= definition that defines it in terms
of even simpler components. For example, A::= B and B::=
C | D means that the definition A is
equivalent to the patterns C or D. |
[A] | Optional element A.
For example, A::= B[C]D means that the definition ABD or BCD. |
A+ | Element A can have
one or more occurrences. For example, A::= B+ means
that the definition AB, BB, or BBB. |
A* | Element A can have
zero or more occurrences. |
A | B | Either element A or B can
occur, but not both. |
(A B) | Element A and B are
grouped together. This is particularly useful when the | operator
is used or when a complex pattern is repeated. For example, A::=(B C)+
(D | E) means that the definition ABCD, BCE, BCBCD, BCBCE, BCBCBCD,
or BCBCBCE. |
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