1.2 Notational conventions and syntax

1.2.2 Macros and special forms

• The macro or special form name appears in a fixed-width font.

• A word in italics indicates a syntactic type that is included in the macro or special form definition (for example, var, declaration, tag).

• Braces, { and }, enclose a group of symbols. A star (*) that follows the braces indicates that what is enclosed can appear any number of times or not at all. A plus sign (+) indicates that what is enclosed must appear at least once.

{x}*

zero or more occurrences of x

{x}+

one or more occurrences of x

• Brackets, [ and ], indicate that what they enclose is optional and can appear only once.

[x]

zero or one occurrence of x

• A vertical bar (|) indicates that either of the elements separated by the bar can appear, but not both of them.

• The symbol ::= means "is defined by." It indicates that the term on the left side is defined by the expression on the right.

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