in logback-ecs-encoder/src/main/java/co/elastic/logging/logback/EcsEncoder.java [170:178]
private void serializeMarker(StringBuilder builder, Marker marker) {
if (marker != null) {
EcsJsonSerializer.serializeSingleTag(builder, marker.getName());
Iterator<Marker> it = marker.iterator();
while (it.hasNext()) {
serializeMarker(builder, it.next());
}
}
}