HHH-16130 Add javadoc for dateTrunc

hibernate-core/src/main/java/org/hibernate/query/criteria/HibernateCriteriaBuilder.java

@@ -998,6 +998,18 @@ <Y extends Comparable<? super Y>> JpaPredicate between(
 	@Incubating
 	JpaFunction<Float> second(Expression<? extends TemporalAccessor> datetime);
 
+	/**
+	 * Truncates a date, time or datetime expression to the given {@link TemporalUnit}.
+	 * Supported units are: {@code YEAR}, {@code MONTH}, {@code DAY},  {@code HOUR}, {@code MINUTE}, {@code SECOND}.
+	 * <p>
+	 * Truncating translates to obtaining a value of the same type in which all temporal units smaller than {@code field} have been pruned.
+	 * For hours, minutes and second this means setting them to {@code 00}. For months and days, this means setting them to {@code 01}.
+	 *
+	 * @param datetime the date, time or datetime expression to be truncated
+	 * @param temporalUnit the temporal unit for truncation
+	 *
+	 * @return the truncated value
+	 */
 	@Incubating
 	<T extends TemporalAccessor> JpaFunction<T> truncate(Expression<T> datetime, TemporalUnit temporalUnit);