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7.1.3.2 Sequences and Groupings ¶

A sequence consists of elements usually separated by space or newline characters. A sequence element can be:

• An input sequence where each element can be a terminal symbol, terminal symbol placeholder, or terminal symbol class. See Input. The input sequence can be a named terminal symbol segment.
• A put-back sequence where each element can be a terminal symbol, terminal symbol placeholder, or terminal symbol class. See Put-Back. The put-back sequence can be a named terminal symbol segment.
• An output terminal symbol. See Output.
• A nonterminal symbol defined anywhere in the grammar by a production or copying assignment. See Nonterminal Symbols.
• A specifier. See Specifiers.
• An expression grouped by ‘(’ … ‘)’.

Use ‘(’ … ‘)’ to group elements into a single unit. You can use ‘(’ … ‘)’ to group:

• sequence elements;
• sets of alternatives separated by ‘|’;
• loop bodies quantified by ‘*’;
• optional expression bodies quantified by ‘?’.

A grouped expression provides context for the specifiers #su… and #d. They do not affect expressions outside of a group ( … ) containing the specifiers. See Switching Spur Update Mode and Deferring a Terminal Symbol, for more information on the specifiers.