The FIRST set for this parser, or the empty set if the production goes to \epsilon.
(parser: StringAdd).+(other)
(parser: StringAdd).self
(parser: StringFormat).self
(parser: ArrowAssoc[Parser[R]]).x
(Since version 2.10.0) Use leftOfArrow
instead
(parser: Ensuring[Parser[R]]).x
(Since version 2.10.0) Use resultOfEnsuring
instead