+ * Since ICU4C 63, start date of each era is imported from CLDR. CLDR era data
+ * may contain tentative era in near future with placeholder names. By default,
+ * such era data is not enabled. ICU4C users who want to test the behavior of
+ * the future era can enable this one of following settings (in the priority
+ * order):
+ * <ol>
+ * <li>Environment variable <code>ICU_ENABLE_TENTATIVE_ERA=true</code>.</li>
+ * </nl>