in lib/src/parser.dart [137:151]
AstNode? _parseOptions() {
if (!_scanner.scan('{')) return null;
if (_scanner.matches('}')) _scanner.error('unexpected "}".');
var options = <SequenceNode>[];
do {
options.add(_parseSequence(inOptions: true));
} while (_scanner.scan(','));
// Don't allow single-option blocks.
if (options.length == 1) _scanner.expect(',');
_scanner.expect('}');
return OptionsNode(options, caseSensitive: _caseSensitive);
}