Map keyword identifier

%{}:
Tuple operator

Lex `{}`as TUPLE_OPERATOR.  It can be used as a value.
Tuple keyword identifier

{}:
Quote keyword identifiers

Keyword identifiers where the a Char List or String is before the COLON
to allow for interpolation of the atom in the keyword identifier.
Bit string operator

`<<>>` lexed as BIT_STRING_OPERATOR, which is a `value` in the parser.
Bit string keyword indentifier

<<>>:
Comparison operator keyword identifier

`!==:`, `===:`, `!=`, `==`, and `=~`.
Fix order choice for keywordIdentifier

Keep choice elements in alphabetical order.