code: func yaml_parser_parse_flow_sequence_entry_mapping_key(parser *yaml_parser_t, event *yaml_event_t) bool {
  	token := peek_token(parser)
  	if token == nil {
  		return false
  	}
  	if token.typ != yaml_VALUE_TOKEN &&
  		token.typ != yaml_FLOW_ENTRY_TOKEN &&
  		token.typ != yaml_FLOW_SEQUENCE_END_TOKEN {
  		parser.states = append(parser.states, yaml_PARSE_FLOW_SEQUENCE_ENTRY_MAPPING_VALUE_STATE)
  		return yaml_parser_parse_node(parser, event, false, false)
  	}
  	mark := token.end_mark
  	skip_token(parser)
  	parser.state = yaml_PARSE_FLOW_SEQUENCE_ENTRY_MAPPING_VALUE_STATE
  	return yaml_parser_process_empty_scalar(parser, event, mark)
  }
docs: //
  // Parse the productions:
  // flow_sequence_entry  ::= flow_node | KEY flow_node? (VALUE flow_node?)?
  //                                      *** *
  //