Fix UuidPatternConverter docs (#3768)

Author: julianladisch

log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/UuidPatternConverter.java

@@ -22,7 +22,7 @@
 import org.apache.logging.log4j.core.util.UuidUtil;
 
 /**
- * Formats the event sequence number.
+ * Formats a UUID.
  */
 @Plugin(name = "UuidPatternConverter", category = PatternConverter.CATEGORY)
 @ConverterKeys({"u", "uuid"})
@@ -39,10 +39,19 @@ private UuidPatternConverter(final boolean isRandom) {
     }
 
     /**
-     * Obtains an instance of SequencePatternConverter.
+     * Creates an instance of {@link UuidPatternConverter}.
+     * <p>
+     * The {@code RANDOM} option generates a Type 4 (pseudo-randomly generated) UUID.
+     * The UUID is generated using a cryptographically strong pseudo-random number generator.
+     * <p>
+     * The {@code TIME} option generates a Type 1 (date and time based) UUID using the local network interface's MAC address.
+     * To ensure uniqueness across multiple JVMs and/or class loaders on the same host, a random number between 0 and 16384 will be associated with each instance of the UUID generator class, and included in each time-based UUID generated.
+     * See {@link UuidUtil#UUID_SEQUENCE} how to seed the UUID generation with an integer value.
+     * Because time-based UUIDs contain the MAC address and timestamp, they should be used with care.
      *
-     * @param options options, currently ignored, may be null.
-     * @return instance of SequencePatternConverter.
+     * @param options An array containing either {@code RANDOM} or {@code TIME}.
+     * If empty, {@code TIME} will be used.
+     * @return a new {@link UuidPatternConverter} instance
      */
     public static UuidPatternConverter newInstance(final String[] options) {
         if (options.length == 0) {

src/site/antora/modules/ROOT/pages/manual/pattern-layout.adoc

@@ -1339,15 +1339,19 @@ Includes either a random or a time-based UUID
 .link:../javadoc/log4j-core/org/apache/logging/log4j/core/pattern/UuidPatternConverter.html[`UuidPatternConverter`] specifier grammar
 [source,text]
 ----
-u{RANDOM|TIME}
-uuid{RANDOM|TIME}
+u[{RANDOM|TIME}]
+uuid[{RANDOM|TIME}]
 ----
 
-The time-based UUID is a Type 1 UUID generated using the MAC address of each host
+The random UUID is a type 4 UUID. The UUID is generated using a cryptographically strong pseudo-random number generator.
+
+The time-based UUID is a Type 1 (date and time based) UUID generated using the MAC address of each host.
 To ensure uniqueness across multiple JVMs and/or class loaders on the same host, a random number between 0 and 16,384 will be associated with each instance of the UUID generator class, and included in each time-based UUID generated.
 See also xref:manual/systemproperties.adoc#log4j2.uuidSequence[`log4j2.uuidSequence`].
 Because time-based UUIDs contain the MAC address and timestamp, they should be used with care.
 
+TIME is the default.
+
 [#format-modifiers]
 === Format modifiers