Example
edit

With the following input:

{"Records":[{"key": "value #1"},{"key": "value #2"}]}
{"Records":[{"key": "value #3"},{"key": "value #4"}]}

Without setting expand_event_list_from_field, two events will be forwarded:

{"@timestamp": "2022-06-16T04:06:03.064Z", "message": "{\"Records\":[{\"key\": \"value #1\"},{\"key\": \"value #2\"}]}"}
{"@timestamp": "2022-06-16T04:06:13.888Z", "message": "{\"Records\":[{\"key\": \"value #3\"},{\"key\": \"value #4\"}]}"}

If expand_event_list_from_field is set to Records, four events will be forwarded:

{"@timestamp": "2022-06-16T04:06:21.105Z", "message": "{\"key\": \"value #1\"}"}
{"@timestamp": "2022-06-16T04:06:27.204Z", "message": "{\"key\": \"value #2\"}"}
{"@timestamp": "2022-06-16T04:06:31.154Z", "message": "{\"key\": \"value #3\"}"}
{"@timestamp": "2022-06-16T04:06:36.189Z", "message": "{\"key\": \"value #4\"}"}