Understanding Log4J2 exception(throwing) output

I'm trying to make sense about the output of throwing field of Log4J2 output.

This code deliberately generates an exception and sends the exception to Log4J2:

class HelloWorld1 {
    private static final Logger logger = LogManager.getLogger(HelloWorld1.class.getName());

    public void method() {
        try {
            System.out.println("Division: " + (1 / 0));
        } catch (Exception ex) {
            logger.error("Got exception", ex);
        }
    }

Examining the log output, I get something like this:

{
	...
	"level": "ERROR",
	"loggerName": "logforj2.HelloWorld1",
	"message": "Got exception",
	"thrown": {
		"commonElementCount": 0,
		"localizedMessage": "/ by zero",
		"message": "/ by zero",
		"name": "java.lang.ArithmeticException",
		"extendedStackTrace": [
			{
				"class": "logforj2.HelloWorld1",
				"method": "main",
				"file": "HelloWorld1.java",
				"line": 23,
				"exact": true,
				"location": "classes/",
				"version": "?"
			}
		]
	},
	...
}

So far so good but I see examples online showing a different output for an exception and those outputs have much more fields than I was expecting:

{
	...
	"level": "DEBUG",
	"message": "Msg",
	"thrown": {
		"commonElementCount": 0,
		"localizedMessage": "testIOEx",
		"message": "testIOEx",
		"name": "java.io.IOException",
		"extendedStackTrace": [
			{
				"class": "org.apache.logging.log4j.core.layout.LogEventFixtures",
				"method": "createLogEvent",
				"file": "LogEventFixtures.java",
				"line": 56,
				"exact": true,
				"location": "test-classes/",
				"version": "?"
			},
			{
				"class": "org.apache.logging.log4j.core.layout.JsonLayoutTest",
				"method": "testAllFeatures",
				"file": "JsonLayoutTest.java",
				"line": 105,
				"exact": true,
				"location": "test-classes/",
				"version": "?"
			}...
		],
		"cause": {
			"commonElementCount": 27,
			"extendedStackTrace": [
				{
					"class": "org.apache.logging.log4j.core.layout.LogEventFixtures",
					"method": "createLogEvent",
					"file": "LogEventFixtures.java",
					"line": 53,
					"exact": false,
					"location": "test-classes/",
					"version": "?"
				}
			],
			"localizedMessage": "testNPEx",
			"message": "testNPEx",
			"name": "java.lang.NullPointerException"
		},
		"suppressed": [
			{
				"commonElementCount": 0,
				"localizedMessage": "I am suppressed exception 1",
				"message": "I am suppressed exception 1",
				"name": "java.lang.IndexOutOfBoundsException",
				"extendedStackTrace": [
					{
						"class": "org.apache.logging.log4j.core.layout.LogEventFixtures",
						"method": "createLogEvent",
						"file": "LogEventFixtures.java",
						"line": 57,
						"exact": true,
						"location": "test-classes/",
						"version": "?"
					},
					{
						"class": "org.apache.logging.log4j.core.layout.JsonLayoutTest",
						"method": "testAllFeatures",
						"file": "JsonLayoutTest.java",
						"line": 105,
						"exact": true,
						"location": "test-classes/",
						"version": "?"
					}...
				]
			},
			{
				"commonElementCount": 0,
				"localizedMessage": "I am suppressed exception 2",
				"message": "I am suppressed exception 2",
				"name": "java.lang.IndexOutOfBoundsException",
				"extendedStackTrace": [
					{
						"class": "org.apache.logging.log4j.core.layout.LogEventFixtures",
						"method": "createLogEvent",
						"file": "LogEventFixtures.java",
						"line": 58,
						"exact": true,
						"location": "test-classes/",
						"version": "?"
					}...
				],
				
			}
		]
	},
	...
}

My problem is, I don't understand most of the fields.
For example:

1. Why is it called extendedStackTrace? Is there any other stack trace that is not extended? What is the difference?
2. What does commonElementCount mean?
3. What is the difference between localizedMessage and message?
4. What does cause field mean?
5. What does suppressed field mean?

1. What you see in the output depends on the Layout you have chosen and how you configured it. The PatternLayout describes 3 different types of Throwable PatternConverters; the default ThrowablePatternConverter, the ExtendedThrowablePatternConverter, and the RootThrowablePatternConverter.

The difference between these are:

• The default ThrowablePatternConverter prints a stack trace just as you would see it from Throwable.printStackTrace() (in fact, that is how the output is generated).
• The ExtendedThrowablePatternConverter includes the name and version of the jar for each line in the stack trace. This can be quite helpful when diagnosing problems.
• The RootThrowablePatternConverter prints the innermost "caused by" exception first followed by each of the Throwables in the chain. In other words, it prints the Exceptions in the reverse order of the ThrowablePatternConverter so that the exception at fault is printed first, which can save some time.

From your example above it looks like you are using the JsonLayout. That Layout formats its output using Jackson and specifies that the LogEvent includes an ExtendedStakTrace, which would include the jar and version information.

2. It is almost true that when exceptions are chained the each exception will have stack frames that are common with the exception it is chained with. Once the first common element is found all the rest to the bottom of the stack trace are almost always in common as well. This field identifies how many elements are in common with the predecessor allowing the common elements to be not be printed.
3. localizedMessage and message are documented in the java.lang.Throwable.
4. cause is the next Throwable in the chain. It is also documented in java.lang.Throwable.
5. suppressed is a set of exceptions that were suppressed. Again, see java.lang.Throwable.