In this International Standard, formal syntax is described in a manner
similar to ISO 8879 with the following exceptions.
A sequence of expressions indicates that the expressions shall occur in the order shown. The , operator is not used.
The occurrence indicators ?, +, and *
have higher precedence than sequencing, which in turn
has higher precedence than the connectors | and &.
For example,
a b | c d*
is equivalent to
(a b) | (c (d*))
A syntactic-literal is indicated by a monospaced typeface as shown.
syntactic-literal
In a syntax production, double square brackets (
) can be used to surround
an or group. The meaning of this is similar to an and group. However,
if any of the members of the or group have a * or + occurrence
indicator, then they can occur the number of times indicated but
intermixed with other members of the group. For example,
a* | b+ | c | d?
means a sequence containing only a's, b's, c's,
and d's in which
any number of a's occur, one or more b's, exactly one
c, and at most one d.