assistance-engine/docs/developer.avapframework.com/chapter9_15.md

6.2.3. Parenthesized Forms

A parenthesized form is an optional list of expressions enclosed in parentheses:

parenth_form ::= "(" [starred_expression] ")"

A parenthesized expression produces whatever the expression list produces: if the list contains at least one comma, it produces a tuple; otherwise, it produces the single expression that makes up the list of expressions.