Any sequence of rules may be grouped using parentheses (()). The parenthesized sequence can then be modified as a group. Parentheses also delimit sets of choices separated by pipe (|) characters.
A group can also be delimited with curly braces ({}), in which case an implicit optional whitespace-matching rule will be inserted between rules sequenced within the braces.
Examples
USING: prettyprint peg.ebnf ;
"abcca" EBNF[[ rule="a" ("b" | "c")* "a" ]] . V{ "a" V{ "b" "c" "c" } "a" }
USING: prettyprint peg.ebnf ;
"ab c
d " EBNF[[ rule={"a" "b" "c" "d"} ]] . V{ "a" "b" "c" "d" }